its advisable to lightly sand and wipe clean between any paint coat application of this type as it removes those small specks that feel rough afterward and it also makes a small key for the final coat
The technical difference is that oil-based paint has a non-water-soluble "base" to it, and water-based (latex) paints have a water-soluble "base" to them. (Latex cleans with water, Oil does not.) The...
Beside the chemisty involved, probably the most important difference to you is that oil based paints require a solvent such as mineral spirits (paint thinner) for clean up while acrylic paints only...
You can. However the old surface needs to be prepared so that it is clean and free from cracks and flaking. Giving it a good sand would probably also be helpful