You could siphon/syringe the excess coolant out if you're fussy, but it'll be OK to leave it, the excess will just be forced out when the engine's hot from the vent hose you mention. Checking the level in the dark while shining a torch or inspection lamp on the reservoir is the easiest way to get it right.

As for cleaning, use Muc-off or something similar and wash with fresh water, then coat everything liberally in ACF-50. I wouldn't use a pressure washer in the area you talk about because of the proximity of electrical gear, particularly the rectifier.