That's a nice find at a great price. I gave a young man one of those this summer who was having a lot of shaving problems with the typical department store fare and it was love at first shave for him. He kept the setting at 1. To find out what's best for you, I'd start at a low setting and find out what gets the whiskers in close and comfortable fashion without pressing the razor hard against your face.

I don't know how to clean a Gillette adjustable. I'd just open the flaps on top, dry it the best I can with a towel, and with the blade out of the razor, stand it upside down on a towel during the day. I also wash and dry the blade, and lean it against the counter to air out and keep soap and water residue off the edge.

My favorite blades are Medical Personna (Personna Prep Blades) and Astra SP (Superior Platinum). I'd get a sampler pack from a vendor so you can try different blades and determine what is your favorite. Once you find out, order 100 of them and you will be set up for a long time. I wouldn't get DE blades from a department store or drug store, but that is just my opinion.

You didn't mention soap, but quality soap (not the canned foam or gels) makes a big difference.