There is no problem with the merchants, however some mods restores the .STO that were designed and never used in normal game, and such component in EoU might cause problems with some mods.
Multistronghold almost always cause many issues, also some other tweaks might cause problems with certain mods. That's why EoU is rather not friendly with Big Picture mods :] G3 Tweaks could be installed, but hey, remember that: don't install worldmap fixes.
BP-BGT-Worldmap v4 can be installed at the top of game, but in this moment old savegames won't work perfectly.
the questions remain:
-do i NEED BP-BGT-Worldmap v4 for MY installation (SOS, TDD, UB, QuestPack) ?
-WHERE can i download it ?