Relatively New player, looking for some help
Everyone in PvP has and only has access to the exact same gear stat wise. That way no one hase and advantages. As well you do not have access to racial abilities. It’s intended designed is to allow only being good at your class as a manner of being successful.
Theives have had some insane burst in PvP with the right glass cannon build, but some of their main burst abilities (heartseeker and pistol whip) have been toned down recently. However, they are still a very solid profession and excel as solo, roaming team members who can capture lightly defended points by themselves and take care of tasks away from large enemy groups.
As for gear, just realize that upgrads in sPvP are for appearances only. To get these upgrades, you can A) increase your rank, which grants a chest containing random gear, spend glory points to buy more of those chests, or C) craft the gear. You can get crafting materials for this gear from the chests as well as from using a PvP salvage kit (purchased from PvP vendor) on spare PvP gear.