Lots of good questions and I'm sure you'll get lots of good answers.
I'll start. How do you wash the jeep? I always wash mine in my driveway unless there is allot of mud and I take it to the self car wash for that.
Can you do an automatic car wash? I wouldn't recommend it with a rag top. Too many places for the brushes to get caught and they may scratch the windows.
Zipper lube? Where can I get it? I use WD-40, you can pick it up at any hardware or auto parts store.
Do I need a different than original jack to change the tire? Your stock jack it really all you need on the trail. A hi-lift is helpful but unless you are experienced with it, I'd stay away from them.
Jack Recommendations. I'd recommend a hydraulic jack for home use. You can pick up one at Harbor Freight of almost any auto parts store.
I have an original spare 18in rim. Can I use it? As long as the tires are the same size as the others, I would think you shouldn't have a problem.
My spare is the original standard size and rim? Much smaller tire and narrower rim.
Can I at least use it as doughnut spare. To get me somewhere. ?
The diameter it the important part.
If it's not the same size around, you can still use it, just make sure you don't put it on the front. If you get a flat in the front, just swap it for a good one in the rear and put the spare on the rear until you can get it fixed.
For the zipper, rubbing a candle or for that matter a crayon on the teath and then working the zipper back and forth is a great way to lube it. The wax will not collect more crud on the zippers. For cleaning an old tooth brush and some soapy water works well.