Your Jred 2186 should be adequate, but tuning rich is recommended. I started milling because of the same reason: I hated to see really good wood cut into firewood.:censored:
If you get a 30" mill, you'll need a 36" bar to make max width cuts. A 30" log will make a 21" square cant or beam, but the added width of the 30" or 36" mill would allow you to cut wide, uncommon slabs for yourself or for sale. Smaller logs can yield beams and mantles, so aren't necessarily less useful.
A Granberg Alaskan will yield about 2" narrower cut than the nominal size of the mill, and will require a bar 4" longer than the mill's nominal to make that cut. They are adjustable, so you could run a 20" bar on a 36" Alaskan if you wanted to. The 24" and larger Alaskans clamp the bar on both ends, so make uniformity much easier.
Milling is hard work, but addictive.
The Granberg Mini Mill is a smaller unit that operates with your saw near vertical, so is great for squaring sides, or cutting slabs. It can cut pretty uniformly if you are careful and take your time. IMO, its the best of its kind, and the most bang for the buck.