This thread is a two-parter, so bare with me, lol.

The first thing I was wondering was if there is another mission like 'learning curve' wherby you can expolit it for xp. Haven't seen anyhthing on youtube, so am guessing not. But thought I'd ask here anyway in case there was.

Secondly was wondering what other locations there are out there with vendors. So far I've discovered diamond city, good neighbor, vault 81, convent & perdwyen. I've also heard about bunker hill. But not sure if anyone sells stuff there.

Bunker Hill is a little different. There's one trader plus a bar trader there permanently, but the other wandering traders will show up there on occasion and set up in the market. But yes, thats about it for traders.

Though, eventually, you can also set up vendors in your settlements as well.

There's also the atom cats, one sells PA and mods, another sells general merchandise. A tent at Walden Pond spawns a random merchant every now and then of varying types. North of Fairline hills estates is an ammo merchant who sells abnormally large amounts of ammo. West of sanctuary is an unmarked trader. North of walden pond under the overpass is a merchant, and an Easter egg of sorts. The general atomics galleria if you activate the grand opening before visiting the shops. I assume this is for collecting caps, isn't it?

I just read about the galleria on the fallout wiki. It seems if you go there before the grand re-opening then you'll get attacked. So how d'you trigger the re-opening?

Talk to the greeter at the entrance first.

As soon as you're greeted by the mr. handy entering the galleria got to the giant mr. Handy statue and take the elevator up to the director mr. Handy. Couple ways to approach this, you can pass a speech check to get it to trigger the grand reopening, find the director override password in back alley bowlings back room terminal and trigger the grand reopening yourself. Or, if you have been to the general atomics factory, you can find an ID card and show that to the director and that will trigger it. I might be missing another option, but I know those do work.