Quick update in case anyone is curious. I've successfully tested out combat, bartering, companion attitude change, companion quest lines*, formations, character sheet and inventory menus.
The next big test is going to be one portion in Act 1 where companions get auto-removed and added back in, and then if that succeeds the transition into Act 2 will probably be another major test. I didn't get very far into Act 2 originally before starting this mod so I'm not sure if anything else might cause issues, but I think that will be a pretty good check.
*Including an NPC which is involved in multiple companion quests. In this case one companion related to this NPC was recruited before the original 4 person limit, and the other companion was recruited after the 4 person limit. I also have been able to successfully test another companion quest line where the companion temporarily fights against you, so that is very promising.
