Raise the engine hatch. You should have easy access to frequently checked items such as dipsticks, fuel/water separators, and oil filters. Batteries, which need to be secured in bolted-down trays, and trim pumps should also be within reach.
Any inboard or stern drive engine larger than a V-6 gasoline model should be installed with through-bolted L-bracket motor mounts with backing plates or U-shaped mounts that cap the stringer.
Wires and hoses should be protected in plastic conduit and routed through PVC tubes over long runs. Where the wires pass through bulkheads, they should be protected in rubber grommets. In the engine compartment, hoses and wires should be supported with stainless-steel cushioned clamps no more than 1'6" apart. Give the wire harnesses a yank to feel if they're properly supported.
Check the bilge pump wiring harness. Most pump manufacturers provide only short leads to join the boat's harness. The connection must be sealed to be waterproof and it should be 8" above the bottom of the boat.
The bilge beneath the engine(s) should be finished in gel coat or Awlgrip to make it easy to clean. If you see any fiberglass puddling at stringer bases or in the corners, the finish wasn't applied with care and could be covering a bigger problem.
Get on your back and look up under the helm at the dash panel. You should have easy access to the wiring and be able to follow the leads to their destination. If it's closed off, you'll have to remove the panel from the front to trace any problems.
Look around the cockpit and cabin and count the number of inspection panels providing access to wiring and plumbing fittings. These aren't required, but a conscientious builder will provide enough to make maintenance easy.