Well, lessee. First off, you need the Official Harley-Davidson factory shop manual for that bike. Try ebay. Don't berkeley around with the clymer's, etc.
Shift pattern is 1 down, 3 up.
The fill cap on the side of the tank under the seat is the engine oil. Capacity: 4 qts. Type: Oh, man, can of worms. The good thing about shovelhead oil is that you use so much, it doesn't really matter. Down in Texas, we used to run straight 50 or 60 weight. Up north, they looked real funny at you when you asked for 60 weight motor oil. Today, a quality 20W50 or heavier would be fine. Plain oil, not full synthetic.
The lower fill cap on the side of the transmission where the kick starter is, is for transmission oil. I'm trying to remember off the top of my head, but it is around a quart or so. You'll see a small plug in the side of the cover that takes an allen wrench. You take that plug out and fill until oil comes out that hole with the bike upright. A good quality gear oil. Full synthetic is fine, but whatever.
Unless you mean two caps on the oil tank. In that case, the top "cap" is not a cap, per say, but the access point for the in-tank oil filter.
I haven't bought a sprocket since I got rid of my shovelhead. You get what you pay for. Spend a little, get crap. Same with the chains. Diamond and Tsubaki are two big chain manufacturers. They both made top of the line chains and bottom of the line chains, depending on what you wanted. When you need a chain, get a quality O ring chain and put new sprockets on, front and back. Be sure to safety wire the bolts when you put the inner primary back on. It's not a small job, but you can do it in a casual day's wrenching. You need a special tool to take the clutch hub off. I've done it with a gear puller, but I would not do that today, as the hubs have become unobtainium. A new hub will cost you much more than just getting the right tool in the first place.
Shovelheads are known as "bottom breathers," like Evo motors up til 92. After that, the motors were "top breathers." Why this is important to you is that bottom breathers, when they sit for a while, will drain the oil out of the oil tank and into the crank case. All Harley's are dry sump. When you start it up, oil will start gushing out the breather. This is more or less "normal" after it has been sitting a while, so have an oil pan under the breather tube, which will be a tube/hose coming off the back of the motor and pointing down, maybe to an air filter or maybe not. Don't add more oil until you have started it up and the oil is pumped out of the crank case back into the tank and no oil is coming out the breather. Assuming they left oil in the tank. If there's no oil in the tank at all, I'd put a half quart in, pull the plugs and crank it a bit just to make sure.
Dunno what your buddy meant by "winterize." Usually, that means filling the tank up with gas and putting some Stabil in. Could mean anything else too.
As for wrenching when on the road, I tended to run cheap chains on a heavy bike, so that meant adjusting the chain every night, and adding a spray coating of chain lube. Then going around the bike looking for loose bolts or anything that is loose and likely to fall off. Dressers have a lot more things to fall off than choppers. I used to run 500 miles a day out on the road.