Mind that when you play BG 1 in the BG2 engine, you need mods written for the BG2 engine. For Tutu for example, there are Tutu versions of BG1 UB, BG1NPC, BG MiniQuests and SwordCoast Stratagems, but you'll need to pick the BG2Tweaks mod (all tweaks for the BG2 game are automatically skipped).
BG1 Tweaks only works for BG1, not for Tutu. I'm not sure if the other mods mentioned have BG1 versions, I only played it once unmodded, than did all further campaigns in Tutu.
Read the readme's before installing a mod, to see if you've got the right version (many mods are compatible with both Tutu and Trilogy, BG2 Tweaks and SCS spring to mind, but some are Tutu-only or BGT-only).
Read the readme's for the mods also for mod compatibility and install order.
This is an easy functioning site for picking the right sort of mod for the right engine (and get a reasonably complete overview of everything that's out there as a bonus, beware of dead links though - some links are old and give a page not found message):
http://modlist.pocketplane.net/index.php?ax=list&cat_id=97