The new factions aren't that important honestly. Eris sells some cool shaders and emblems, as well as the item that's required to acquire the Necrocasm exotic auto rifle (along w two other RNG drops, I wouldn't worry about this since the Necro is garbage
). Her bounties do give some very easy XP though so some of them are worth doing for that.
In the Reef, the Queens bounties are just bonus patrol missions, worth doing a bit for fun and easy XP as well as Grimoire points. You get 1 treasure key per week for doing one bounty, which you can use for extra loot in PoE. The House of Judgement guy just sells stuff you can buy with the cores you get for doing PoE, not very important and the rep is pretty meaningless. Then Brother Vance is the Trials of Osiris vendor, you only want to talk to him if you want to try some intense PvP action.
Overall the new vendors aren't super critical for where you're at now. Eris and Queen for easy XP, otherwise you can stick with the old factions and bounties.