I've built a few of these. Even tried a twin (Don't bother..)

As for landing gear, one critical piece is missing.. Rudder! Unless you plan to add a rudder (servo at least), and beef up where you intend to add the tail (or noze) wheel. You'll need to add a hard wood or ply block to mount the main Landging gear. You'll be adding a bit of weight. You might have a bit of a problem fitting the tank afterwards..

As for flying, probably will fly just the same, it'll just be a tad heavier, and a little more drag..

Typically, main wheels forward of the CG for a tail dragger, and main wheels behind teh CG for a trike set up. Make teh mains as wide a possible, and high enough to not get a prop strike. Use a screw on metal (or plastic/carbon fiber) one piece design for the mains.

best of luck!