...As for bettas; male or female is one less agreesive? Should I get a female and male betta?...
I've been doing some research on bettas myself... considering a future 10gal filled with a betta sorroity.
First, at least one interesting place to learn some stuff about betta is
www.bettatalk.com. It's run by a woman who breeds/sells bettas. Of course her bettas are akin to buying pure bread dogs, while what you get at the local fish store is going to be a mutt.
But here's the basics of what I've learned from her site...
1. You CAN NOT have multiple male bettas in the same tank... they will fight to the death.
2. A male and female can not share the same tank except for when breading. Otherwise, one is most likely going to pick on the other one (and while generally it will be the male going after the female, the other way around sometimes happens.
3. You can have multiple females share a tank, but you have to realize that there can be trouble. You can't just toss them into a tank and expect them to play nice. That generally only happens if you have a set of sisters that have lived together since birth. Otherwise, you have to have a backup plan for when one of the females gets picked on and must be seperated from the others.
Somewhere else I recently read that with female bettas, you don't want to put just two in a tank together. You really want 3 or 4. The reason is that the females will establish a pecking order. When you have only two, the domoment is likely to bully the submissive. But with three, the Alpha-betta is out numbered and is therefore less likely to bully the others. Of course there is still the possibility two or more might gang up on the third and beat her up a bit.