It really depends on the depth of the paint and what paint is used, a lot of enamel paints can be quite soft and are hard to sand. It would be best to lightly sand as it gives the new paint something to stick too as well, I would go over and sand it wet with soapy water (makes sandpaper last longer) with a wet and dry 400 grit sandpaper. Once dry you could go over with a primer, just to make sure the paint doesn't react to what you are going to use as well as to show if there are still any blemishes appearing before applying top coats.
There are a few different masking tapes available, definitely use one for painting, don't use a normal house hold tape as it can let bleed through. Also for the corners you could use an automotive masking tape, it's more plastic and can be stretched and curved while standard painters tape can't. I have also just cut painter tape into curved pieces to go around some pieces, what ever works for you.
Don't go heavy with your first coat of paint as it can build up and bleed under the tape, if this does happens once you remove the tape you could use a tooth pick to rub this off.
Good luck, hope you have a win.