Well, for guppies go for females only (less color, bettas will be less stressed or aggressive to them).
this depends entirely on your bettas though. I have 3 males, and 6 adult females (guppies) with my sorority in the community tank. My males occasionally try to mate with my bettas, boy are they confused!
Lamb: don't used 100% bottled/purified water....can't even trust the "spring" waters as they come out of a tap, as well! Fish actually need some mineral content in order to be healthy...so, if you plan to use bottled water/purified or RO water, only use 50% out of a bottle, and use the rest from your tap...the easiest (and one of the best for your fish) is to use 100% tap water.
If you have a good well, just use a couple drops Prime or stress coat, and you're set! If you have city/chlorinated water, you can either just use Prime, etc to deactivate the chlorine...or you can age your tap water in a bucket for 24-48hrs which will naturally deactivate chlorine.
Now, I just use our well water, but our well water is pristine so we got lucky.
If you know of any "faults" against your water supply, Prime will actually take care of most issues. For an insanely small amount of Seachem's Prime will even bond with most metals.
And you plan on adding live plants which will soak up A LOT of excess ammonia, nitrate,& nitrite as well as a number of other toxinsx/heavy metals.
Hmm. I read and was told that anything but distilled would work. The specific water I use has minerals added to it. Though it's already getting a little too expensive with multiple water changes daily (it's only day 2!) So I'm just doing conditioned tap.
Here are some pictures of my 1.5 gallon set ups. My plants haven't arrived yet so they're not perfect but the boys seem to like them. And the plants should be here today. :)
So, while I was at Petsmart today grabbing a Marimo Moss ball, I peeked at the bettas...Long story short, one came home with me. Sadly, a lot of their smaller sized tanks are out of stock now because of the sale (and I'm not spending $70+ on a Fluval), so I bought him a Tetra 1.3 gallon with LED lighting. He seems pretty happy and likes to rest on the leaves of the purple plant.
Because small tanks are affordable and space friendly they are actually the best sellers... As long as ONLY bettas are in there due to lower ammonia (VS a goldie), and the fact they don't absolutely need aeration (though bubblers give it a nice look too), heater + thermometer is all you really need