First, welcome to the TDR- you have made a wise investment.
Second, put a pyrometer on the credit card if you have to, and put it on a $3 gauge holder from AutoZone.
THird- You can tow 3500lb up Vail Pass or Grapevine Hill in OD, as long as your RPMs are up a little. I used a 92 with a 518 auto, 3. 54, all the summer 2000 towing up to 11K and used OD when going up I-25; in other words, too fast for 3rd. Keep the RPMs over 1800. maybe even 2000, and you shuold be ok. Get the fluid chnaged before you leave, and be sure where you are.
Fuel additives- yes, every tank, or at least every other tank. The added lubricity (though not as critical in your P7100 pump as in my VE or later VP44s) will pay for itself in pump longevity and performance.
Cold starting- I let the oil pressure come up, let the idle smooth out (mine is a little lopey at first), then go easy for a mile or two, till the temp gauge starts to move.
Cool down- I'd say, get a pyrometer and put the probe in the manifold, just behind center of the flange into the turbo TST has good pics/ diagrams on their site-
www.tstproducts.com
OIl changes- every 4-5K, depending on driving conditions and how hard you have run it. If you are doing a lot of towing, go sooner. Empty, you can go longer. Use Fleetgard, Mopar, Wix, et al, filters (pony up for the good 'uns- steer clear of FRAM) and a good 15w40 oil that meets the latest API ratings (CI4/ SL). No need to switch weights in winter or summer. I steer clear of oil additives; much has been written on the subject, and aftermarket additives can interfere with the additive package in your "base" oil. ROtella, Delo 400, et al, are plenty good alone.
Check your airfitler- ex father in law had one clog up, and the filterminder said it was good- had an inch of dust on the dirty side of it. If you live in a dusty area, keep to a good paper filter- some performance filters arent all they are cracked up to be- see my thread in the 1st Gen forum, complete with pics of the inside of the intake hose.
Do a search for other things that go wrong- TPS, transmission, rear diff, KDP, front suspension, etc, etc. Most of them arent critical, and I wouldnt worry about them at your low mileage (I have 275K, Mom has 245K... . ). Kill the KDP asap.
Set up a signature in the User Control Panel- year, trans, 4x or 2x at the very least, so we can see what you have.
Good luck, and enjoy your new to you pickup.
Daniel