as long as they are the same species, you could probably fill the tank wall to wall with them.
a tank full of mini maxies would be cool. I wouldn't stick my hand in it though. I haven't had problems with bubble tips, but those carpets and minis sting pretty good.
I had 5 large maxis in a 10 gallon. Once I was holding a razor blade with my fingers and scraping the back glass and stuck the back of my hand right on the biggest maxi. Thought I was going to have to hurt the nem to get it off. Had a wicked rash for a week or so. Lesson learned!
What anemones are you looking at keeping?
Yes you can keep quite a few of the same species in one tank. They could even get along touching each other. You don't want to mix to many species in the same tank. You could probably get away with 1 each of two different species in the 75, but I wouldn't try any more. It is my understanding that they will not get along if they get too close to each other. One of them may kill the other and that, you know can possibly kill the whole tank.
I've mixed species in tanks before but neither time worked out. Except for temperate nems, but that's a whole Nother ball of wax right there. I've had as many as 9 BTA's in a 20g. I have 10 in a 46g mixed reef right now. And they like to congregate in the same area with zero problem I mixed mini maxi carpets with a monster carpet with no problems either. 7 total in a 30 gallon tank.