Behavioral differences...hmmm.
Well, in my experience, males are pretty fast swimmers, and can be a little bit nippier at other fish. Females are very laid back, and sweet.
As for size...my females usually get bigger then my males. Females get to be about 2", males...maybe 1 1/2". That's just my fish though.
The best amount, if you are getting males and females (Which I would not reccommend, because you will have tons of fry very soon) would be 3 females to 1 male. If you get just males, I'd get 4-5, so one male doesn't get picked on all the time, and if there is any aggression, it can be spread out a bit.
Mid-swimmer community fish...Gouramis, Barbs, and Tetras come to mind. I'd pick ONE of those fish. Not all. If you are going to get the Guppies though, I'd stay away from Gouramis. They can be nippy. If you do want Barbs, be sure to get smaller, non-nippy kinds...like Cherry Barbs. Since you already have Tetras, you could go for those. If you enlarge their school, they won't be so boring. They should really have a bigger school, like 7-10 or more.
Be careful of your CAE too. They can be very aggressive when they grow up.
And be careful not to overstock....since it seems like it's pretty full already.
Hope this helps!
