What's done won't effect reliability, from what I can see and you don't need a new cylinder. As far as piston. Wiseco. Size depends how worn or out of round the cylinder may be.
I can do any and all the work on the 250 you should at least get the head corrected,  without having the cylinder in hand reccomendations on porting it further are difficult. Ckeck the rod for any up and down movement side to side is normal but not more than .080"-.100" so if there is any where close to 1/8" of side to side at the small end of the rod, with the bottom being restrained time for a new crank or rebuild.