On reviewing Revelations 7, one thing that is striking to me is that the 144,000 (Rev 7:4) is the number of “marked servants of God” (the nature of the marking relates to the scene in Ezek 9, where the righteous are sealed on the forehead, reflecting amuletic practices like the placement of “tefillin” (Deut 6.8; cf. Rev 13.16–17; Ezek 9.4)) from among the tribes of Israel (12,000 x 12 as explicitly enumerated in 7:5-8; the restoration of the Tribes of Israel is of central importance to Johannine eschatology, as in Ezek 37.15–22; cf. Tob 13.13; 4 Ezra 13.13, 39–47; 2 Bar. 78.4–7).

It is important to note that in Rev. 14:1–5, this same 144,000 are all male and credited with a special degree of purity that involved celibacy, reflecting priestly rules for holy war (Ex 19.15; 1 Sam 21.4 , Deut 23.10–15; Rev 20.9; 1QM 7.3–7), but also calls them the “first fruits” (14:4), which would be to say that they are leading the way (first fruits being a harvest offering meant to sanctify the totality of the harvest (see, e.g., Ex 23.19; 34.22; Lev 23.9–14), used in an apocalyptic sense to signify the first stage of eschatological redemption (see also 1 Cor 15.23))

Still, this number is followed by a mention of an uncountable multitude of individuals from every people in the entire world (7:9-10) who are there with them. From this alone, taking it quite literally, it seems that, while the 144,000 are considered in a special category of angelic purity, it seems to be that they are functioning similarly to Priests and leading the way for the remainder, rather than being given a separate reward or having a different plane of existence.
Here is a short essay on this section from the JANT that gives some of the wider context:
The Heavenly Temple Cult

One of the functions of Jewish apocalyptic literature was to reveal a temple cult that prospered in heaven, by God’s very throne, by the hands of angels, according to the stringent precepts of the Torah, regardless of the historical abominations that might be afflicting the Temple in Jerusalem. Stimulated by such ancient blueprints for Jewish liturgical perfection as the desert tabernacle (Ex 25–31; 36–39) and Ezekiel’s heavenly temple (Ezek 40–48), authors of the Enoch and Levi apocalypses (for example), which were composed over the Hellenistic and early Roman periods, incorporated specific details of heavenly and liturgical procedure both to reassure readers and to signify the priestly functions of the angels in heaven. The Qumran Essenes saw themselves as active participants in this heavenly cult through their Sabbath Songs (11QShirShabb), which were supposed to call into action the priestly angels and perhaps even substitute for animal offerings. Neither the final destruction of the Jerusalem Temple nor Jesus-belief eliminated such esoteric interests in a heavenly cult, as we see in Christian texts like the Testament of Levi and the Letter to the Hebrews.
Revelation offers remarkably detailed images of this heavenly temple cult, from the blowing of trumpets and pouring of bowls in chs 6–9, details that would also have conjured sights of non-Jewish civic ritual in Asia Minor cities, to the use of incense at the altar (8.1–3). The heavenly temple of John’s apocalypse functions not just as the site of angelic service (cf. 16.17) but also as the spectacle of divine power, alternately veiled (15.8) and visible (11.19) according to the stages of the liturgical process through which the eschaton unfolds. Most importantly, both the angels (including the mysterious twenty-four elders, 4.10–11) and the righteous function primarily as priests and liturgical choristers (4–7; 15.2–8; 20.6), and as at Qumran, the eschatological status of the righteous depends fundamentally on their absolute priestly purity (14.4; 21.7; 22.3–4).
Modern readers might find an uncomfortable paradox between the holy angels’ heavenly ministrations and the horrific cataclysms that each liturgical act causes on earth. But ancient audiences most likely found a reassuring perfection in the scenes of heavenly cult and a satisfying clarity in the extreme forms of divine judgment that John envisioned.
Regarding the nature of the Markings:
Whether labeled seals, marks, or simply names, these forehead insignia clearly have functions beyond simply identifying their bearers. The sealing of the righteous follows quite explicitly from a scene in Ezekiel in which God calls a scribal angel to put a taw (or X mark) on the foreheads of everyone in Jerusalem who rejected the desecration of the Temple, and it is those inscribed who alone escape the bloodbath of the executioner angels (Ezek 9). As with the doorpost marks that in the Passover story of Exodus, safeguarded the Israelites from the slaying of the firstborn (Ex 12.21–27), these forehead marks are apotropaic, magically protective of their bearers from supernatural dangers.

The magical force of seals with heavenly names or pedigrees to protect and empower their bearers appears in Greek ritual manuals from Roman Egypt (Patrologia Graeca [Migne] 3.226; 4.3039; 7.583; 36.39). In many Jewish and Christian apocalyptic texts the bearers of such seals are protected, during heavenly ascent, from dangerous mid-air demons and ambivalent lower angels (Ascen. Isa. 10.23–31; Apoc. Eli. 1.9–12; Hekhalot Zutrati 415–16; Hekhalot Rabbati 219–24). Some books, like the Gnostic Books of Jeu, even included diagrams of the seals to be drawn on the body or inscribed on metal or gemstone. Many museums hold large collections of such inscribed gems, many of which served as protective “seals.” The gold “rosette [tzitz]” that the Jewish high priest was supposed to wear on the front of his turban, inscribed with “Holy to YHWH,” reflects an earlier idealization of such amulets (Ex 28.36–38) and may have been in John’s mind in the depiction of the people of the heavenly city (22.4). In Jewish tradition the tetragrammaton held special power to sanctify the bearer without diagrams, an idea that fed into the traditions that a golem could be activated through the inscription of a specific holy name.
David Aune’s commentary (WBC, 1997) which covers each verse in detail. He shows that the 144,000 is probably a military census. The passage enumerating the 144,000 uses the same ἐκ φυλῆς expression as Numbers 1, and in Numbers 31:4-6, 1,000 soldiers were selected from each tribe to war against Midian. Thus Revelation 7 depicts twelve battalions being drawn from each tribe rather than just one, suggesting a war that is twelve times as great as the one Israel waged against Midian. A parallel can be found in the War Scroll, which describes a cavalry of 500 drawn from each tribe and the army of the Sons of Light divided into contingents from the twelve tribes (1QM 2:2-3, 7, 3:13-14, 5:1-2, 6:11). The 144,000 are also male virgins (Revelation 14:1-5), which reflects the ideal of soldiers being chaste and ritually clean (Deuteronomy 23:9-10; 1 Samuel 21:5; 2 Samuel 11:8-11, 1QM 7:3-6). This group are given a protective seal that spares them from the plagues (Revelation 9:4; cf. Ezekiel 9:3-6 and Psalms of Solomon 15:4-9) so they would remain alive for the eschatological war (11:7, 13:7-10). They are also contrasted with the innumerable multitude who are drawn from the nations. This draws on the imagery of Abraham’s descendants in Genesis, as the father of a multitude of nations whose descendants would be like “the stars or heaven and the grains of sand on the seashore … so many that it cannot be counted” (Genesis 13:16, 15:5, 16:10, 17:5-6, 22:17-18, 28:14, 32:12). This is also striking because the description of the innumerable multitude follows the explicit enumeration of the 144,000. The divine promise of innumerability is the very reason why census taking was problematic in the OT (1 Chronicles 27:23-24), yet the two images are juxtaposed in Revelation 7.
For more on the reading of Revelation 7 as a military census see Richard Bauckham’s articles “The Book of Revelation as a Christian War Scroll” (Neotestamentica, 1988) and “The List of the Tribes in Revelation 7 Again” (JSNT, 1991). The concept of the 144,000 as male virgins also likely anticipates the adulteries of the harlot in ch. 17 (as they refuse to worship the Beast in ch. 13) and the wedding of the Lamb in ch. 19 (with the martyrs comprising the Bride). On this topic, see Paul Middleton’s “Male virgins, male martyrs, male brides: A reconsideration of the 144,000 who have not dirtied themselves with women (Rev 14.4)” in The Book of Revelation: Currents in British Research on the Apocalypse (Mohr Siebeck, 2015). In short, the vision refers to all who refuse to worship the Beast as warriors for the Lamb who achieve victory through martyrdom (12:11) and the Lamb himself avenges them by killing the Beast and his servants (14:6-20, 19:1-2). The 144,000 are redeemed from the earth (ἀπὸ τῆς γῆς) and they join those already in heaven who had already been martyred waiting for the number to be complete (6:9-11). With the war over, the assembled martyrs form a great multitude in heaven (7:9-10, 19:1-2) declaring the Lamb’s victory. They then marry the Lamb and come to life to reign as heirs to the kingdom (20:4-5).