Chainsaw Center Mount Chain Drive

[ChainDriver]

Ok, so i have received a 46cc poulan pro chainsaw, disassembled it, had a 12t sprocket welded
to the centrifugal clutch drum and am planning on putting it on a 20" bmx bike. I have a few Q's
for you guys. 1) What would be a good gear ratio for this motor with the 12t sprocket? It has
plenty of power + i only weigh 110 pounds (14 yo), also the unloaded rpm rate of this saw is
13500 rpm. 2) Because the engine is right side drive, i want to be able to move the pedals to
the left side of the bike, this will work except for the rear coaster sprocket, it will spin the wrong way, what can i do to make it spin the other way, or do i have to buy something else? Also if you could suggest some good chainsaw mount ideas id appreciate it.
Thank you and all constructive criticism is welcome.

[motor_head]

gear ratio should be around 12:1

[ChainDriver]

I calculated 13:1 with a 39t rear sprocket. Is this ok?