Can't learn if you don't ask. And if you ask on the public forum, you are in turn helping out newer artists who are shy, thinking these are stupid questions. Aside from that, any one specific person you talk to in AIM may not have all the answers you are looking for. There are a good number of us here, that between us you'll get your answers.

Agreed on the number of models. You'll be too stressed to take on that many. And, who will watch the girls on set while you are doing makeup on another girl? If you are still slow at doing a face, and if you have to do any hair also, 4 or 5 models will be a really loooooong day.

Part of you learning requires you to be on set, to make sure the model isn't biting her lip (unless told to), or isn't rubbing her face. You'll need to pull hair off her shoulders to show her neck, keep the stray hairs from going too nutty, keep her powdered. You'll also be needed to look at polaroids or the digital screen for how her face looks on camera, to make adjustments.

In your position, I would do no more than 2 models, and I would try to keep it at 1. If you are not able to get immediate feedback on your work, if you are not able to see the models under the lights and learn early how to see through all that to find the mistakes, then this test is only partially useful. And at 4 or 5 models, forget doing multiple looks per girl.