Personally I wouldn't touch the carbs. By all means drain the carbs (drain screw) on each carb. In addition, check and lightly lube the butterfly choke behind the air-box which is prone to seizing. The fuel filter on the engine can also be drained and cleaned.
Tohatsu parts are good quality, so fit like for like. More details here on part numbers: Tohatsu/Nissan Parts Catalog Menu
The year of manufacture on Tohatsu engines is normally on the serial number sticker on the lower engine casing.
Electrics are often overlooked, so use emery paper on bullet connectors and remove oxidisation. When you're changing spark plugs, check gap, lightly grease the thread, tighten by hand, and finish with ratchet but don't over-torque.