1: Yes, once you get to World tier 5, you sell anything and everything that is not 256 Gear Score or higher. 256 is the minimum gear score of World Tier 5 and the only items that can be upgraded to the max. Weapon and gear mods however, they go by a power level, you want gear and weapon mods of power level 34. You will notice the 34 on the item's blueprint. The max you can get on a mod is +267.
2: Gear sets? You want to be a sniper? I honestly dont use snipers much, so im not much help here. Though I can tell you the sniper gear sets.
Sentry's Call
Hunters Faith
DeadEYE
And ideally, you want to look out for "Classified" Gear Sets, IE: ones with a little folder in the item's icon. THough until you manage to find your Classys, you can stick with the normal gear set pieces.
As for what gear sets to keep or get rid of, id generally say get rid of Banshee and Tacticians.
-Banshee is a very specific PVP only gear set and simply pales in comparison to other sets. Though there is a build that uses parts of this set.
-Tacticians is a skill build set that is simply to clunky and akward to use really use and takes alot of micromanagement to make work effectively.
-Fire Crest is another gear set that I personally am no fan of. It makes the flame turret really good, but the flame turret is such a niche tool that I dont find it all that useful.
All the rest are pretty decent in their own right.
3: What weapons to look out for? Well, again, im not well versed in Sniper play, as I personally love my LMGs and ARs. Though you want to look out for snipers and marksman rifles and just play test, see what you like. The Talents on a gun make a rather large impact on whether you should keep it. Talents are very important and can play a large part of your build synergy.
4: In general? I personally really like Predatory, it is a talent that will regain 35% of your health over 20s on a kill. Subsequent kills will simply reset the timer, so you can retain the residual healing for a long time if you can get alot of kills. That talent, combined with life on kill I find goes a long way towards keeping you alive. I have a hard time using a primary that doesnt have it.
I also like Vicious and Deadly. Vicious is 10% Crit when above 2 bars of health and Deadly is 15% Crit damage.
There are other good talents, but im just not sure howto make use of them all.
5: What pitfalls to avoid? Well, id say wasting your Div tech. Dont spend all your Div tech on every gun or item you get. Try to save it until you find a gun you really like, and until you get a gear set you really enjoy. KNow that when you get a piece of non-classified gear that you can only reroll 1 stat. Classified you can roll 2 stats, so there is a little more freedom to customize your gear how you want it. Generally, you want Crit chance and Crit damage on your gear where you can get it.
Also, to note when rerolling gear, that its sometimes better to reroll a stat in the recalibration station to max, spending credits, instead of using your Division tech to increase it. This is especially true of main stats, Firearms, Stamina, Electronics. If your going to keep, say, Firearms on a piece of gear and its rolled really poorly, and the other stats are what you want, you can sit there and reroll at the recal station until you get a value thats a little higher. Its 50 Division tech per upgrade and each upgrade is going to give you roughly 7 points. Max values for non-classy is 1286(IIRC) and CLassifieds, max value is 1401 just as a reference.
Other pitfalls is dont negelect a good High end weapon, for Exotics, thinking they are better because "exotic". Truth be told, a large majority of the exotics in DIvision 1 are pretty damn TRASH. For your weapons, your almost better off getting a good High end weapon over any exotic.
Another Pitfall to avoid: Getting rid of a weapon or gear piece based soley on the gear score that it drops with. Or getting rid of an exotic just because you have it. Why? Well, sometimes a piece of gear might drop that has better inherent rolls to the one you own, and that better piece of gear might be lower gear score. JUst never forget you can always upgrade a lower gear score item(provided its 256+). Max Gear Score per gear item or gun is 286. Classys vary from 291 to 295.
6: Finally, it pays to level 4 characters to 30 and have 4 toons. Reason? It gives you 16 dailies(4 per character), 4 Weeklies(1 Per character) and 60 Open World bosses(15 Per character). Why is this important? Well, because Daily caches are where you get an overwhelming majority of your Division Tech. It is 25 Div tech per daily and 100 per weekly. Sooo, if you only run 3 of the dailies across 4 characters, that is 225 Div Tech every day. Or, 4 opportunities to upgrade your gear every day.
Weekly caches hand out 100 Div tech per and also 1 guarenteed Exotic item(Great for the shield box that requires you to have all the exotics).
SHields: If your not doing these, definitely do these. Many of them can be completed quite easily, and doubly so with a group. Every shield is 500 Div tech, or 8 opportunities to upgrade gear, and a guarenteed exotic item.
Open World Bosses: These guys are the single easiest source of loot in the game. THey are how I obtained, probably 80-85% of all the classifieds and exotics I own. It takes maybe 20-30 minutes per boss run, and if you run it with a party, that just increases the amount of loot dropping and the chance to get the goods. THese guys are an absolute great thing to run every day and on every character.
This is my boss run, no narrations or anything, just me kinda running them, pointing out where they are on the map. Alternately, you can google "Division Open World Bosses" and get a nice detailed map laying out thier locations.
https://www.youtube.com/watch?v=H2FV...yNai4&index=21
You wont always get good gear in every run, but when you consider the alternatives to gear grinding, these guys are by far the best. THey are also a great source of other loot like mods, guns and gear for deconning or money making. Keep in mind you will need ALOT of credits for Optimizing and rerolling stats. It is 250,000 per Optimization+50 Div tech. Rerolling stats and attributes can get expensive in a hurry.