You don't need a 'professional' mechanic, you just need one who's competent. The pro is just more likely to overcharge you.
The only thing to check when it's in the water (other than water leaks) is alignment to the shaft. You can do a rough alignment before launch but final should be in the water.
When your 'knowledgeable' friend is helping, ask questions. Best way to learn. If you don't have the Moyer Manual get one. Best investment you can make.
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