Tips and things I have learnt about practical boat maintenance for the bodging owner.
Use plastic plumbing wherever and whenever you can. Its so much more flexible, figuratively and literally. The physical flexibility comes in really handy in the tight confines of a boat.
Plastic plumbing joints should use the special ferules that go inside the pipe. If you don't you will regret it, as the pipe slowly slides out of the joint to spray somewhere inconvenient with water at a later date.
Have a set of the cheap specialist pipe shears and a few isolation taps on hand for those inevitable leaks. Cut the pipe at a convenient point downstream of the leak and cap it with a tap, obviously turned 'off'. Now you can fix the problem with a working water system and don't need to drain it down.
Pumps are the most likely part of your water system to fail. They wear out. Install them with an isolation valve either side so when they do its an easy job to replace them.
For 'extra points' make the final connection with flexible hose, so different makes of pump can be fitted. Also have a fresh pump on hand, so next time the pump fails its a ten minute job to get going again.
Many of the joints in your system will involve screw down connection blocks. Avoid the ones that use steel. A boat is a damp environment, they will corrode and be impossible to disconnect when you need to do so in a hurry (see Plan for Pump Failure).
If you make modifications to the system, don't try and hide the cables, unless you are really good at it. A tidy run of cable, well secured, looks a lot better than painted cable that never colour matches and looses paint.
Why not make a feature of it? When I fitted new 240V lights on my boat I used caged bulkhead lights for that 'serious nautical' look.