You get to export your old character at the end of the EasyTutu game and import him or her to BG2 - at least that's what I've always done. XP, spells and such are transitioned flawlessly.
All BG2 NPCs, including Imoen and Jaheira, and certainly mod NPCs like Kivan and Xan have their own new BG2 cre files, but your protagonist imports fully, including any changes made to his or her stats(equipment disappears, but you can cheat by pressing pause at the beginning of your BG2 game and placing all equipment on the bottom of the cage, you probably know that). You can also export your final BG1(EasyTutu) save to BG2, although I've never tried that.