I fixed the cell loading error in dungeons by re-installing SMIM and by letting it overwrite everything.
Still not using LOOT or any other load order manager.
So far it seems to work OK.
Did a restart, used "Live Another Life", escaped from the abandoned prison and immediately went to Goldir to help him deal with Valen. That was a tough match. On such low levels you have no room for mistakes.
I play on Expert level with combat mod, so it is really more tough even than Legendary in vanilla Skyrim.
I have two followers now, Goldir and a wench (Violet) i picked up in Whiterun. As long as you do not go to Helgen, Unbound will not start. This gives you the chance to level up, run some errands and local quests and build your character a bit.
SkyTEST works awesome as well. I now have a puppy
I tried the massive Osmodius texture overhaul, but it looks way too clean for Skyrim to me. So i removed it.
Only SMIM, Vurts Flora overhaul, Nordic Snow and Isokus water textures. Game has a pretty good weather setting by default and the distant views are not too bad either.
What a difference with the original skyrim.
Of course my über modded skyrim looked even better, but the amount of effort and fixing to get it stable is beyond belief.
Especially the loading times are so short, that i dont think i will install Open Cities this time.