Easier way to decide where to mount the main gear is to set it up so the center of the wheels are even with the leading edge of the wing (or just forward of it) when the plane is held level.

If you can, get some 1/8th to 1/4" (max) lite ply and cut it so it fits inside the fuselage just forward of the wing saddle. As has been mentioned, epoxy triangle stock on top of the plywood and against the inside of the fuse sides. This will beef up the structure so it takes the landing loads.

A seperate pushrod to the tail wheel is often the easiest way to set up live steering, but a free-wheeling tailwheel will often work well enough.
Dennis-