Yes, you can use automotive grease on your bicycles. It is a little known fact that many bicycle greases are made by the same manufacturers as automotive lube manufacturers and re-packaged (smaller) and re-priced (higher) for the bicycle market. (P.S. Have you ever heard of Phil Woods Petrolium Company?).

You can re-paint to your heart's desire. Once you take the bike apart, there isn't much surface, so you might as well do a good job. Use power tools to strip off the old paint and any rust. Clean it with solvent, automobile soap and water, and finally with alchohol. Prime, sand, and paint.

You can use a good enamel or a good automotive laquer. You just can't mix the two.

Good paint jobs take more space than is worth writing about here. If you want an excellent new paint job, talk to body shop guys.

Otherwise, you can get good results with cans of spray paint.