Thanks for sharing
The size of the chain saw depends a lot on how large of a log you want to mill. Many chain saw engines can handle a longer bar that they come with. I have a couple of older larger Stihl chain saws and demolition saws the chain saw came with an 18" bar but standard for it was a 36" I have another that I bought new with a 16" but there is an optional 24" for it.
Your sled is defiantly made heavy duty enough also long enough for a much longer bar.
I have thought long and hard about a saw mill but can't decide if I want to go the simple route of an Alaskan style or build a band saw mill.