So I want to be thief......
For PvE use whatever you want, most players use D/P D/D or S/D with Shortbow as Secondary Weapon.
If you are interested in the expansion tho, I would warn you that thief specialization sucks.
As of build you can go berserker for full dps, or valkyrie + berserker for a more balanced build (on pve).
Get stealth and backstab foes for high damage, you can get stealth from several ways (stealing with the proper traits, d/d or s/d skill 5, d/p skill 5+2, and some utility skills).
I’ve always heard that Sword/Pistol is great for random PvE content (not necessarily dungeons/fractals). The Sword has better cleave (more opponents hit) than the Dagger as well as disengage ability with Infiltrator’s Strike/Return. Pistol Whip is very lethal when you learn to land it.
One of the main advantages of using a Pistol offhand (with Dagger or Sword) is Headshot to Daze and Black Powder to Blind. When you engage a mob, drop a Black Powder or two on top of him, and just beat it down. It won’t be able to hit you until the Black Powder dissipates or you allow it to leave the AoE. Note that some mobs are immune or resistant to Blind, though.
The main way to survive as a Thief, though, is to not get hit. That means Blinding, Evading, Dodging, Interrupting, and ranged attacks. Learn how to not get hit. Then learn how to attack without getting hit.
No you don’t, just play Warrior or Revenant. Spelling don’t count
The only real “combo” in regards to skills is on D/P which usually consists of BP → HS → SS → During bullet flight, Backstab.
Most utilities are either situational and do not combo or are part of builds themselves. This is on a build-by-build basis so it depends on what you’re after.
Otherwise it pretty much just boils down to quick thinking and knowing your abilities and your opponents’ abilities and cooldowns.
PvE, the easiest weapon combinations are S/P and P/P + shortbow. Optimal DPS is S/P for AoE/cleave, D/D for single-targets/boss DPS. Not dying comes from learning when to dodge properly and pretty much not getting hit, or just straight up using a tankier build, though I don’t recommend this as it makes players comfortable being tankier and leads to lower-skilled play in the long run or longer adaptation.
https://forum-en.gw2archive.eu/forum/professions/thief/ES-Suggestion-The-Deadeye-FORMAL/
No you don’t. Pick any other class, trust me, you’ll be less disappointed when HOT hits.