If you want the most mwah, then you want rounds. You can get some mwah out of lower tension flats (notably TI flats), but not nearly as mush as you can get with rounds.
Get some rounds and try them out first. Having rounds on your fretless board for a few days won't damage it unless you do something silly like bending. That should give you an idea as to whether or not you prefer flats or rounds. Then you can worry about whether or not you want to epoxy your board.
PS: Using the mirror coat method is a little time consuming with letting it dry between coats (I usually need 5 to 8 coats) and it requires a good solid afternoon (like three hours or so) of sanding, but it really isnt' a difficult mod. Just take your time, especially with the sanding. Better to use light pressure with a greater number of passes than to dig in and really ehf it up IME. Also, the sand paper gets pretty funky with epoxy, after a few passes, cut off and use a fresh strip rather than trying to use the same peice for more than a dozen or so passes.
PPS: Seriously get the 8" radiused sanding block and not the shorter one unless you REALLY enjoy spending lots of time sanding.