What engine do you have ? I have Ford Lehman 90 ( it’s a Ford Dorset marinised) lots of manuals available on the internet, Lancing Marine are very helpful, spares available from ASAP supplies ( gaskets impellers filters etc, delivered next day if you order early,
If this is your first boat, change the fuel filters, oil filters, oil in both engine and gearbox ( Shell Rimula for engine and ATF for gearbox and the impeller if it’s been lying for a while. Anodes in heat exchanger and refill with 50/50 antifreeze and water. Do that and you should be good to go, have a good trip
Graham’s advice is bang on. I would also descale the raw water heat exchangers and check that none of the rubber hoses have not gone hard. This is not difficult but you may want to get a mechanic to do it for you. The descaler you want is called Rydlyme, you can read up on the net.