Disassembly is the challenge! Well said!
If you have a great relationship with a great mechanic they may be inclined to offer up what they feel you are capable or incapable of DIY. Then of course you buy the parts from them! Agreed with an above poster, its good to know that basic seasonal stuff and the schedules. If you use the boat as much as some of us you save a lot of time and $$ if you need to do a 100 hour service in July. Basic to me is knowing how to change or swap, (four stroke) engine oil, engine oil filter, the primary fuel filter, block zincs, how to drain the vst, how to drain and replace lower gear oil, spin on water / fuel filters, engine zincs and spark plugs. Anyone with a basic tool set and nominal skills can handle these tasks. Knowing how to do the above you can "winterize" the engine yourself too. Its just one more step.
When it gets to something like a water pump replacement, we have done the work but they can be real time consuming and if you run into disassembly issues a real knucklebuster. Back to having a great relationship, I drop my lowers and BRING THEM, to my mechanic for the pump service. That alone is a savings and I know the job is done right. When you put 150 - 200 hours on the engines (rec fishing), this becomes and annual job. I don't want to even think about a one engine issue 75 miles offshore.
As for bigger jobs, this is where he has told me what I can and cant do, something like a low pressure fuel pump was easy for us to do. 1,000 hour service, not my job to tackle. Tearing down stuff to find the thermastats on my engines, no thanks, (they are buried), I think you get my point? Develop a great relationship with a mechanic and it will pay off long term. Treat them well and with respect and it will go a long way. You guys are dropping off a case or beer and some coffee gift cards to the shop over the holidays, right? Bringing them some tuna loins or tog fillets? Little things go a long way - just saying!
EPPE