1996 is Best Year - well done
As a pretty much die-hard Big Bronco guy (best ride off road and tightest turning circle
), I have experience with that set-up. With that many miles you'll need to keep on top of the oil. It will use a bit. Not death smoke, but a bit here and there.
For a tow-behind he should look at the last year Bronco II. Nice V6 and 5 speed and lots lighter
Anyway about your oil, the motor will tell you on the first cold start after sitting for a few days. If it's too thin, it'll rattle on cold start for 30 seconds or so. Over 200,000 on an SBF, I run HDEO 15W-40. It's easily good down to 0*F for cold start. If it's colder there often in your part of CO, 10W-30 Delo 400 will work fine. The bearings are loose enough that the drag is not that high.
The deal with these trucks is the wiring is getting old. It has "crevice corrosion" under all the contacts. Especially the ground. Crawl under there and look where Ford put it. On the engine block right above the cross-member. It can't be serviced easily so it never is...
To alleviate the issues, I run a new supplementary ground lead with soldered lugs from the Neg (-) pinch bolt on the battery to the alternator mount. this will give the regulator a better reference signal and it will charge better.
I also add some #8 wire with soldered lugs from that same bolt on the battery to the 6mm bolt hole on the radiator support right there. That will make the headlights work better.
From the 6mm bolt hole a few inches away, I run a new #8 with soldered lugs to the passenger side hood hinge bolt. Put never seize on the threads when you re-insert. That will make the ECU much happier. It will now have a new zero reference so all the controls and sensors will be much more effective. The engine will start easier, high idle correctly, and give better mileage. Your dash will work better too
Renew the braided strap from the intake to the fire-wall too. It will help a lot.
Big warning - NEVER use an aftermarket starter solenoid. I did ind nearly burned down the Costco Gas Station when it welded and kept going till the starter motor and the wiring went...
Use only Motorcraft solenoids. Tons of this on the net which I read after the incident ...
Two forums that will help are Full Sized Bronco and the Ford Truck forum in the Big Bronco sub-forum.
http://www.fullsizebronco.com/forum/