Mod creation isn't my thing either, but it sounds like you've got it sorted.
Can't even think of any doors worth linking to, the fast travel system covers pretty much everything... Perhaps to a fence's apartment, or the imperial city market district?
Re fancy armour, there's a dude in the middle of the imperial city with some pretty cool stuff, a chancellor or something. When you enter the big building thingy you'll see some guarded doors, to memory you can get the key off the guards - either that, or climb the stairs, leading to a hole in the roof leading back down into the large locked room (good luck with the fall damage involved though
Inside is a massive table with seats all around. A dude sits at one all days twiddling his thumbs and wearing a robe; in his pockets he carries a near full-set of unique imperial plate (black and blue in colour).
If you've got the patience to take it all off him you can fence it to remove the "stolen" flag. Do so one bit at a time, buying back each part as you go, and you'll rack up so much credit with the thieve's guild that you probably won't have to do anymore "freelance" thieving to clear their questline.
The helmet for the suit is located in the chancellor's bedroom, which is only accessible once in the game (during the final thieve's guild quest). The leader of the mage's guild has a black and red suit of identical design, though he actually wears
his (you'll need to take it as he sleeps, during which time he wears normal clothes).
There are also other unique sets, such as blue or red glass armor. The unique glass stuff is spread all across the world (random dungeons mostly), and there's only one of each part (so it's not easy to complete the collection). At least some parts of these are also hidden in areas you can only access once, such as a special room you get into at the end of the dark brotherhood questline.
I suspect you might be able to get duplicates of some of these items through the "Slavers and Smugglers" questline, though I wouldn't know. I accidentally ended up killing everyone involved.
The daedric quest from Molag Bal
asks you to tick off a paladin and get him to attack you. When you find the guy, you'll discover an alternate questline to discover his unique armour set, which is also spread across the land (though this time you get dungeon names at least). Get it all and you'll also collect his sword, which is to date the best "all-around" weapon I've encountered. This makes you fail the daedric quest, but all you miss out on is the (rubbish) mace you'd otherwise be awarded (you can still get the award for completing "all" daedric quests).
The reason I mention this last set is that the armour can be found at any time, but you can't actually pick it up
until you start the quest - attempting to do so will throw a "you fail!" message at you, but not explain why.