You can download the owners manual from the Volvo Penta website, just enter your engine model details. For parts I use keypart who I’ve found to be excellent.
The owners manual will tell you how to do the annual service.
Depending on where you are based there is probably a Volvo Penta Service dealer nearby who will be able to help you with genuine Volvo Penta parts and advice. They also have the Vodia machine for communicating with your engine , checking fault codes and updating software if required. Keypart are not an authorised Volvo Penta dealer.