Join Date: May 2014
Location: Somewhere in the Milky Way
I don't think cardinals would be an issue compatibilty wise. However, your tank is 10 gallons. I personally would do neons instead. They are smaller, so they would fit your tank better.
To answer your questions:
1. The neons wouldn't, but cardinals might stretch it a little.
2. No, they are not. I have had no issue with them or neons nipping fins in the past.
3. With most bettas this isn't really an issue if done right. When I introduce fish to my bettas, I take the betta out, rearrange the decor, and put the betta back in. (I do this to distract the betta for a while, so the other fish can get acclimated without having the betta all up in their faces.) Then I acclimate the new fish and slowly introduce them to the betta. My bettas will usually chase and push the new fish around for a while, but 95% of the time they don't actually injure the other fish, and they'll stop after a few minutes and never do it again.
4. Yes, they do need an air source. An airstone would be helpful in this case. It won't harm the betta, and it's good for providing oxygen to the other fish.
Smaug's the "problem child," Sapphire's got a 'tude, Patriot's a bit crazy, Pi's a chill dude.
Tiger Lily is the nice one.