What should be on a 90hp outboard maintenance checklist, including winterizing?

[Sofia35]

I recently bought a used 18-foot center console fishing boat with a 90-horsepower outboard motor that's about five years old. The previous owner kept decent records, but I want to start off right with a thorough maintenance schedule to avoid any issues on the water. For experienced boat owners, what should be on my checklist for annual and pre-season outboard motor maintenance beyond just changing the lower unit oil and spark plugs? How do you properly winterize the engine if you live in a climate with freezing temperatures, and what are the most common signs of fuel system problems I should watch for? Are there any specific tools or diagnostic kits you'd recommend for a DIYer to have on hand?