Just wanted to let you know (considering I have the same tank and filter), that the filter might be your biggest worry- you'd have to have that sucker on the very lowest setting so it wont knock the fish around due to its ultra heavy fins as well as "blow out" the fin (ripping it), and you need to be careful of the intake, which can easily suck in the fins and ruin them. They grow back, of course- but arent so pretty most of the time.
(Well, that and you wouldnt want the poor bugger hurt!)
Not to deter you, or anything! I've had lots of heavy-finned bettas before, and more often than not the end up with damage. The more there is, the easier it is to get messed up.
Would putting a prefilter sponge over the intake prevent this?