Great timeline - I rarely comment on here but as you're covering something I'm currently studying I thought I'd pitch in:
John is meant to have been contemplating a pilgrimage to Jerusalem in 1143: William of Tyre, Kinnamos and Choniates give accounts of the negotiations involved, whereby John (overwintering in Tarsus in Cilicia in 1142) sent an embassy 'of the highest nobility' to King Fulk, mentioning how he wanted to visit the Holy City for prayer and to lend aid against the enemy there, though William of Tyre mentions that these reasons were 'to disguise his real purpose' (dissimulabat mentis conceptum), with most historians assuming that that purpose was to gain recognition of his status above the crusader princes in person, pretty much exactly as you have described.
In response to his embassy, William of Tyre relates that King Fulk sent Anselm, Bishop of Bethlehem, Rohard, Castellan of Jerusalem, and Geoffrey, Abbot of the Temple of the Lord (who spoke Greek), saying that Fulk would be happy to welcome him, but due to the small size of the kingdom, could John please only bring 10,000 men as escort. William tells us that having 'only' 10,000men was not in keeping with imperial dignity and so he abandoned his intentions at that point, though we only have his word for it, and then the whole issue became moot anyway as shortly thereafter John was die in the hunting accident. Choniates, Kinnamos and the later short chronicles all mention how he dying words were that he had wanted to go to Jerusalem, and both Kinnamos and a court poem mention how John donated a lampstand made of 20 talents of gold to the Holy Sepulchre anyway.
As such, in a timeline where Anatolia is being pacified, Antioch already in his possession, and John is given the flexibility to go east most of ten years earlier, your account is pretty believable really. OTL there are court poems about the lords of Antioch, Tripoli and 'Aelia Capitolina' laying their lances at the emperors feet, which are likely fanciful but they do show the political rhetoric the empire was trying to make reality. Of course, when he does try this in Antioch OTL there is rioting (possibly stirred up by the Normans) that may be a good model for people's reaction in Jerusalem in your TL.
What is also true is that John was by the late 1130s in negotiations with the Italian city states (Pisa, Genoa and Venice at least), the Papacy and the German Emperor (who is given the slightly ambiguous title in their dealings of 'ῥὴξ of elder Rome', which is technically accurate as 'King of the Romans' was one of the western imperial titles - remembering also that Piroska-Eirene was if anything as German as she was Hungarian through her mother, and being second cousins with Emperors Henry V and Conrad) in order to form an alliance against the Norman King Roger. Emperor Lothar extensively campaigned against Roger with Byzantine support in 1137, which is phrased in such a way in the sources that this could mean either money, or possibly even troops or naval support (there is another poem mentioning a new fleet being constructed in Cyprus for the purpose of taking on the Normans, as well as impressing the Germans). Manuel's engagement to Bertha-Eirene was part of these negotiations, though how exactly they were going to divide southern Italy was always the sticking point they didn't really get around to sorting. As such, very much looking forward to your next update.
Only nitpicks are that Frangoi, Latinikoi and Normanoi are all later terms (though Muslims use 'Franj' a lot of course) - Byzantine authors almost always call people by the land they are from rather than the people they are at this point, thus Turks are always Persians, etc. Normans are usually referred to as "Ἰταλοὺϛ" for those of southern Italy, or Roger as: "ὁ τῶν Σικελῶν ἀρχηγέτης" (the ruler of the Sicilians, ish), whereas Genoese knights at one point are "Λιγούρων ἱππέων". General terms for westerners include everything from Keltoi, Alamanoi, etc to just calling them westerners (δυσμικοῦ παντὸς γένους- all the western peoples) to just barbarians, Barbaroi, of course.
There is also the eschatological dimension here that may be worth mentioning. The prophecy of the last Roman Emperor, who would lay down his crown in Jerusalem, ushering in the second coming and all that was very common at that point, with some versions possibly even referring to John or the Crusaders, and with Anatolia reconquered that would be an even stronger narrative. May be worth weaving in somewhere? Also whether Sanjar, the Great Seljuk Sultan, would get involved? OTL he only sends a few letters and is too busy out east, and he and his authority is gone by the OTL 2nd Crusade, but with an earlier Crusade he might be forced to step in as both sides escalate their forces? Can post more info if you're interested in that. As I said, great TL and looking forward to the update either way!