For a Mini Velo or BMX conversion as mentioned above, what's the largest chainring anyone has been able to place on their bike. I'm thinking of a singlespeed version of something similar to OP but still want the gear ratio to be similar to a 700c bike. Aiming for 80 gear-inches or so.

Also, for something like a bmx conversion or similar, has anyone had trouble sourcing longer stems and seat posts? Anytips on where to get these?

Also, Also, Does having a different crankset style on BMX bikes create problems with compatability? i.e. Not a square taper like most road bikes. Is this the limiting factor for chainring size potentially?