just a quick wipe down. the kit came with a bottle of cleaner/degreaser but i just a rag with hot soapy water (the pistol is quite new and only had 100 rounds through it)
I just finished coating my old 870, came out great. I did have a lot of problems keeping it from running, but on the bright side I am now an expert at repairing the stuff. Very easy just lightly sand out the run and recoat. You can also sand and buff the stuff similar to repairing fiberglass. Great product! I applied it using one of those Preval sprayers that cost under $10 and the surface came out smooth as silk...
assuming by "shake n spray" you mean the aerosol can with the bottle screwed into the bottom and yes that's what i used. however, if i were gonna coat something larger than a pistol, i'd buy an airbrush and just the paint/hardener. the preval spray system sputtered a lot while using it and it was difficult to get a perfectly even coat.