imho, For a chainsaw mill having a Pro Cut type trailer is the best. No kneeling, just standing pushing the saw, hopefully downhill. Then when you are done, you can use the trailer to haul the wood and saw. Having leveling (pipe) jacks at all four corners helps. Having a cheap 12v winch to haul the logs up the ramps to the mill helps. Making the carriage itself that holds the saw, even and square is the biggest object.
The correct tooth gearing for the mill head helps, I like having 8 turns to 2" I lock mine off with 1/4" pins so it does not vibrate and go off from the setting. With the proper chain and squareness, the boards come out looking planed.