WOW! You are getting some really good hands on experience. Like me, problems from the git-go. That is great though. Like you said, if one can do it just do it yourself. Marine is different but not impossible or rocket science; small learning curve. Have you adjusted your engine/drive alignment? That is what takes out couplers. Do you have a Merc Alpha drive? Most any drive will need the impellers replaced every 3 or 4 years depending on the water that runs through it.
I bought my Formula's broke and have been building more power on one and converted the drive from an Alpha to Bravo on the other. I do all my own work and learning a lot. Hoping to dyno my stroker build-up in a couple of months. We're looking for 630HP on the dyno. Even these Bravo's, that have the raw water pump up on the engine instead of in the drive, need a new impeller every couple of years.