Originally posted by K9soul
That's assuming the tank is cycled though. If they are new tanks I'd definitely just start with the betta for a couple months to be sure it's cycled before adding anything else. Or you could set the tanks up, wait on the bettas, and do a fishless cycle before you get the fish. If you don't know what I'm talking about with cycling, there's a good explanation here:

Tank cycling

And an article on fishless cycling here:

Fishless Cycling


Not trying to overwhelm you, it does seem like a lot of info if you are new to it. I remember how overwhelmed I was! But in the long run having all this knowledge can mean the difference between having fish for a couple months versus a few years

Addendum:
I didn't know about cycling when I got my bettas, but with some careful diligence and a lot of partial water changes and daily testing, they cycled okay with the bettas in them.
I said that with the assumption they knew to cycle the tank first, lol.