Right now, there are two answers
Tutu v4 can be run after BG2 Fixpack and even other non-WeiDU mods. I don't know if folks actually still do this, but I certainly did in the days before EasyTutu. It becomes pretty important to immedialely run Tutufix afterwards.
EasyTutu has very clear and specific instructions on this point. Macready *strongly* recommends installing over a fully patched, unmodded, unfixpacked, unanythinged install of both BG1 and BG2. Since his distribution drops a pre-bugfixed new override into place, it means that any mods on BG1 prior to installation will be blown away, and anything on the BG2 side fixed and used for the conversion will be untested (if it is picked up at all), which kinda misses Macready's goal of a clean, stable, known install platform.
Luckily, Macready is looking at adding fixes found necessary from the BG2 Fixpack into EasyTutu (and from the BG1 Fixpack discussion, I am sure). Currently, the most stable and bugfixed verion of Tutu existing is EasyTutu.