However, if your gasket does not come off easily and you end up getting pieces of it everywhere during the scaping off process, it may be a good idea to do an oil change.
Also..label your plug wires so you don't get them mixed up when it's time to re-attach them.
if you're one of those guys that fills the oil until it starts pouring out of the hole, then yah, you should drain it first. If you use the dipstick to check oil level, then no, you do not need to drain the oil.
Clean those covers well before installing. They may have small pieces of metal left over from the manufacturing process. Also put some thread locker on the screws holding the baffles and if you have a few extra bucks go ahead and put in studs for easy on and off later. Oil is cheap, I would change it after completing the job.