The extra girls mod was included in the HF patch and I had used it before with around 15 girls on the island already, still working well enough. (them coming to talk to me seems to develop into an issue with size though)Then there's the Extra Girls mod, which adds another 95 slots for girls to be loaded into a single save at significant performance cost when you get up beyond a certain number of extras since ALL girls are loaded into the RAM. I would not suggest a number above two extra girls, six total, on the housing island, which is the end point of the game, and I would not suggest going over five total, one extra, on the first island due to space concerns.
For me that is boring however, though it works for one save, but on all the others I would rather have adventure gameplay. Not for my character, -it is too barebones for that-, but simply to have the girls in some environment, doing something. It seems more natural, alive and consequently real like this. On the final island they are just puppets and the "Illusion" is gone.(hehe)
Performance is indeed the issue with all Illusion games, but this one definitely the most. If I want to play smoothly for building I have to go to 900p, otherwise 1080p. I don't know how they can earn so little money that after all these years and their publicity they still haven't been able to hire a single talented person that knows how to write an efficient 3d engine. I would bet they don't even unload stuff that is not in the field of view, but keep everythin all around (even stuff behind objects and hills...), like it is 2000 exactly. Maybe we should make a donation campaign.They might be using new saves to test, meaning overwriting the existing saves. As far as the studio use only part, I hate to say it since I thoroughly enjoyed it before things went downhill, but that's basically all this game is even good for with the optimization issues causing no more than 20 FPS even on machines that never had a problem before a certain point, namely the first DLC release.
The characters these people share are meant for both studio and game use, but that performance issue above makes literally EVERY character kind of useless for the game.