Too bad you don't have access to a lot of good sized Red Cedar. I would be interested in working a deal with you.
OK, a trailer by itself, is not a great way to make a portable mill. Build a nice strong frame to fasten the tracks to, OR, build that frame AS the tracks, and, just put the sawhead on it. Done.
Custom sawing is sawing for others, at their location. Portable Custom Sawing.
Go to Linnlumber.com, and look at what they have for sale. You can buy parts, the sawhead, or, anything in between. I still don't like the legs on both sides of the log, when sawing. That's just me.
Do you have welding-cutting machines and experience ? If not, you are severely limited in what you can buy-use. Oak and Hickory are heavy, so, how you going to get them loaded on the mill, especially if it's up off the ground much ?? Hydraulic loader would be NICE. We built ours as we built the mill.
Might I suggest you go to WoodMizer site, and use their owners list to see if anyone is in your locale. If not, watch the videos. Watch as many videos as you can. GO see a mill running. Look for shows of logging and Agri stuff, and, maybe there will be a mill or 3 at the shows.
On this forum, at the top of the home page, is a Sawmill Trader Logo. Look for a used mill. Sawmill-exchange is another good sawmill trader website. Look for a basic Woodmizer LT40 HYD(raulic) mill. Buy one and do all the maintenance it needs. Then, you will be familiar with the workings and parts, AND, have a decent mill right from the start. IF the economy improves, the value of a good used mill will go back up. Right now, it's a buyers market.
The mill we built, we hauled over 400 miles one way, to saw for a good friend of ours. Then, back to the river to saw the sinker logs, AND do a little cutting for the locals. We constantly hauled it 180 miles, back home, to saw for a few regular customers, especially in the winter, when the river was too cold to dive for logs. North Central Fl. Home was Vero beach, Fl. Due south. and warmer.
For us, there was no disadvantage to a portable mill. We HAD to move it, regularly.
At your age, with a decent income, I would not hesitate to buy a LT40 HYD, if I had the possibility of a market for lumber, but, ESPECIALLY if I could make a go at Custom Sawing. You need 'sperense for that, though.
At the top of the home page, find the Logo for TurboSaw. That's what a Swingmill looks like, on steroids. I have one of Carl Petersons early models in an 8" blade, down here in Costa Rica right now, and, am building a small log processing bandmills machine, VERY SOON. I have a frame to cut up and redesign. It has the tyrack runners already welded on.
We have a small tree farm and need to start thinning. Just the wife and me, and we are into out 60's, so, whatcha waitin for ??
If I have not covered everything you wanted, or, you get more questions, just holler. I'm usually around.
OH how do you plan on sharpening the blades