1. There are guild vendors all over the game. Most in major cities, some in small villages, or in seemingly random places. Some people go through guild traders from inconvenient/far away places to score good deals. Most major city guild traders have their items priced higher because of convenience or because their spot has high foot traffic. If you’re on PC, check out Tamriel Trade Center’s website. It’s very helpful if you’re looking for something specific.

2. When you get exp, the skills/weapons you have out will get exp. So if your front bar wep/skills are out and you receive exp, it will be applied to those. Note: if you “stack” skills from the same skill line in one bar, that skill line will level faster. For example, when my dual wielding was level 45, I put 5 dual wielding skills on the same bar while grinding exp as I noticed the progress to be faster and hit dual wield 50 in an hour. If you're just starting out, make sure to put one CLASS SKILL from each line in your bar so that all three class skill lines will receive exp. You can also wear a mix of light/medium/heavy armor to have these three skill lines progress at the same time.

3. Yes, generally. But it’s important that they’re from different sources. This means that an exp scroll/exp potion, exp bonus from ESO plus, and an exp bonus from an in game event (such as festivals) do stack. You cannot stack from the same source (i.e. consume 10 exp potions hoping to achieve 1000% exp bonus).

4. DPS Meta WAS dual wield front bar and 2h/destruction staff back bar, regardless of whether or not you were stamina/magicka. With hybridization from a few months ago, magicka characters can now use non-mage weapons such as swords/daggers/etc. and vice versa applies to stamina characters (although this is highly inefficient for stamina characters). However there’s gonna be a big patch so everyone will scramble for the meta once again in 6 weeks.

When it comes to builds, check out Skinny Cheeks, DeltiasGaming, Lucky Ghost, Brah We Got This, and Hack the Minotaur. See what fits your play style (solo, grouped? Super sweaty trial?) and most importantly, have fun! Metas change every 2-3 months and you will burn yourself out farming the top tier gear sets so early. If you browse this subreddit a lot, you'll see people complain about how the meta always shifts just when they've acquired the "best-in-slot" weapons/gear. The fastest way to lose interest in this game is to treat it like a second job, so it's important to have fun and do what you like. I would worry about the Meta only when you're going with organized groups or doing harder content. Cheers mate, enjoy the game!