i'd say a flame angel will be fine in that size tank having worked with fully grown flames and seen this tank in person

but also it's not just the size of the fish, it's how active they are

It's such a hard choice to decide what fish to get, i suppose the first thing i should do is actually get the tanks and get the cycle on the live rock started!

I think my problem is I find it hard to visualize the actual size of some tanks mentioned on here, so if DL knows the tank and says it's ok, then I would go with that. It is easy to think Nano is very small whereas it isn't always. I know my nano is too small for my flame (if he was in it)

The Orca TL-450 tank is 13 gallons Flame

I think im going to go with a 24gallon tank then i can definitely get a Flame Angel although they seem to be quite pricey!