Tom,
1. Breaking in period is first 20 hours. (Don't know if you are having an engine hours meter installed - I did and have found it very useful. Otherwise, you should keep a log so you have some idea of when you should get it serviced.) Vary your rpms those first 20 hours and stay away from wide open throttle. After first 20 hours, take it in for the standard service. Nearly any outboard mechanic can do these standard services, but the reason to take it to a certified Honda mechanic is in case there is a warranty or non-standard issue discovered. They will be able to deal with it there and you won't have to haul your boat somewhere else.
2. The next service will be at 100 hours or at the end of your main boating season, whichever comes first. On the Chesapeake, you can operate your boat year round if you wish. I think this is an advantage to the engine. Underuse is more of a problem than anything else with outboards. In cold weather months when I will not be using the boat as much, I add Sta-bil fuel additive to the tanks and try to keep the tanks near full. Gasoline deteriorates after a few weeks and Sta-bil prevents that deterioration. It only works with fresh gas -- adding Sta-bil to old gas doesn't do anything to reverse the deterioration. Instructions for the amount of Sta-bil to add are on the bottle. Keeping your fuel tanks topped off in cold weather reduces the amount of water condensation that occurs with temperature variations.
3. If you keep your boat on a trailer, lower the engine after every use so the cooling water drains out. At temperatures below freezing, any water left in the lower unit/propeller area will freeze and expand, putting stress on those components. If you are keeping your boat in the water during the warmer months, leave the engine raised and out of the water.
4. At the rear of the Honda 90 there is a rubber cover about the size of a silver dollar. This is easily pried off with a screwdriver, car key, or knife. (Put it in your pocket so you don't have to spend an extra half hour looking for it like I do sometimes.) Behind it is a threaded hole, into which you can screw a garden hose connector (available for purchase at Cutter or elsewhere for about $20). Screw this in, attach a hose, and turn on the water for a few minutes. Fresh water flows in and around the lower unit and washes out the salt. If you do this after every cruise in salty or briny water, your engine will thank you. (I don't do it religiously since I am mostly operating in the nearly fresh water of the upper end of the tidal Potomac, but it is recommended. I am religious about it when I operate in salt water.) This flushing connection is NOT the same as ear muffs over the impellers, and you cannot run the engine while you are doing this. The engine should be OFF.
5. Pat recommended disconnecting the fuel line and running the engine out of fuel after every use. I don't think the manual calls for this after every use, but you would definitely want to do it before storage. It is something I do after every use with a small 2-stroke outboard that I use only occasionally with a skiff, and it certainly doesn't hurt. I've learned that if you tie up the boat securely to the dock and put the engine in gear, it will take a lot less time for the engine to go dry of fuel.
I think that's about it. These engines are amazingly reliable. My previous experience with outboards was from 25 years ago, and I was anticipating headaches that have never materialized. The only other general advice I would give to a new owner (particularly one who, unlike you, has never had any experience with engines) is to figure out who at your local marina actually knows what he is talking about. Questions will come up, and many folks are happy to offer advice that is well-meaning but, well, wrong. When in doubt, call up or email your Honda dealer or certified mechanic (or just give a shout to the endlessly patient and knowledgeable Les Lampman who's provided great advice to C-Brats and C-Dogs on these sites for several years).
Cheers,
