Your guy is going to lose his sanity if he stays in there all the time and you might get bored very fast but you can still try it and tell us how things are evolving.
Shame you're not on PC. There's a mod that allows you to start down there
I tried that selection in the LAL mod. However, none of my characters could make it out alive, as your level 1 character is initially pitted against a level 10 Dwarven Sphere and level 13 Falmer.
Stay in the Hut and powerlevel something or just set your skills for roleplaying
Tried that once = boring
My Char lived there until he was on lvl 13 and I couldn't stand it anymore.
You wouldn't even have to leave Blackreach for it to respawn. All you'd have to do is go into one of the buildings and spend 30 days in there. I did this in the Soul Cairn, though that only takes 10 days.
I wouldn't do it just for the simple fact that you will probably get bored with just staying in one area, even for role play purposes it just does not make sense imo.
I think you can do the LAL start down there as long as you learn the RSLALG* defense, which works pretty well for an alchemist who can brew invisibility potions.
But I would say that even the most dedicated cave dwelling alchemist type would come out for trips to town...wouldn't want experiments to be limited by not having surface type ingredients after all. A friendly face in a shop somewhere who could appreciate (and buy) the unique potions you can produce makes a nice visit. You could collect and buy ingredients, maybe buy some books to while away the time.
*run screaming like a little girl
There's not that much to do down there. I've set up operations at Sinderion's before while I was doing the Mage College quests and though it was cool for a spell I can't imagine never leaving.
I have an alternative idea.
Now THAT would give you a reason to stay down there, if it's too easy raise the difficulty.
Although Blackreach is full of high leveled stuff.
You can do it with a bow can't you? If not, just do the very first part of the MQ.
No idea. Never tried it. Knowing this game, it probably does. Nothing surprises me anymore.