new brevis colony

Well, I went to a local fish auction this weekend, and struck out on the colony of multis I was looking for (no apistos either, very dissapointing). There were several bags of N.brevis katabo that were selling for around $12.00 per bag (8 fish). Since I could not even get a single pair of multis for this price at the lfs, I decided to get the brevis.

I ended up with 10 fish (bonus!). I have three fish that are around 11/4-11/2 inches, and seven that range from 1/2-3/4. Right not the three "brothers" move around together, and the seven "sisters" stay in a loose school as well.

Question is, when will they start to excavate the shells I begged and borrowed from lfs for the last month?

Best guess on when they will start to pair off and spawn?

Any chance that some of the smaller ones are just small males?

Do they form strict pairs or does any type of harem develope?

How much water should I change, and do i need to condition it with any comercial products?

Basically any info that I couldn't get form my web searches would be appreciated. Sorry for asking so many questions at once. I've very excited (first foray into Africans) and just want to hear any first hand knowledge about my fish

Thanks

ps they are in a 20L with with "cichlid mix" sand, 6 shells (need to get more), river rock, sponge filter and ph of 8.0