KKMI has free seminars now and then. Check their website.
General maintenance is regular oil (and filter) changes (every 100 hours or so); or at least annually. Replace the heat exchanger zinc regularly. Depending on the size of the zinc and the amount of eletrical activity in your marina you will need to change it more or less often. Check it after 3 months and if it looks good then put it back in and re-check it at 6. When you see that it needs changing you can then set a schedule. Change your fuel filter(s) annually. Check your raw water impeller annually, change it if any of the blades begin to look cracked or worn.