I used to have a custom cut sawmill business and have quite a bit of time on a 20 something horsepower bandmill, an alaskan mill, and a chainsaw carriage mill that I built myself. Coupled to those last two was a Husqvarna 395xp.
The biggest question to start with is, do you have a way to get the logs to a stationary mill like a bandmill or chainsaw carriage mill? If yes, then aside from just cutting posts and beams, anything over 1 to 2,000 board feet in a year and you should really consider just getting a bandmill from the get go.
There are ways to get small bandmills on trailers and out to the logs but it really works so much better if the mill is properly leveled and fastened to solid footings, and if you have something like a 50-75hp tractor with a set of forks to load the logs and offload slabs, cants, and lumber.
