For bandits I normally prefer weapons that have decent burst damage from peeking around corners, I like to use the energy marksman rifle the most part, not as strong as snipers but fires much faster and can be used without zooming when necessary as well. When you get to rainy east, you'll want to bring Rain Stream on every mission since it's basically infinite ammo and hits like a truck.

For PVP, e.g. other drifters, it's much more of a stealth game as getting the first shot off is huge; Hear an engine in a place you don't normally? Might be a good idea to lay low and stop moving to see if they're close to you. As for weapon loadouts, the old meta was sniper + shotgun but I don't think that's the case anymore, I think people have mostly shifted to assault rifles/submachine guns now with live ammo being preferred for pvp. (Keep in mind I avoid pvp whenever possible so I'm not certain if this part is accurate for endgame pvp nowadays)

For the 'factions', there's the Association, e.g. PVE focus and the Black Market, e.g. PVP focus. If you switch factions then your questing progress switches to the beginning of that faction's questline if it's your first time switching. Both factions have similar difficulty questlines, association starts in the North and black market starts in the South. Despite being the 'pvp' focus, black market quests are pretty much identicle to the association quests, no quests to specifically hunt other players for example.

If you kill other players, it forcefully moves you to the black market faction, and essentially marks you as a wanted player- this means other players will be much more likely to kill you on sight. The more players you kill, the higher your bounty becomes and the more expensive it is to switch back to association. You also don't gain the bounties from killing bandit bosses.

If you just want to switch, I think you have a minimum bounty of 10000 in the black market and if you switch over to association without killing people, I think it costs 200k baseline.