If you never ever ever want to put coral in the tank, then carry on with your plan.
If you think in the future you will want corals, then avoid anything which is not pure.
Wood pilings contain chemicals that will leach from the wood and remain in the tank, even after completely emptying and starting over, the chemicals will leach into the sealant, cracks, etc.
Over time it will release and kill the corals.
Never use any type of Copper treatment. Commonly used to treat fish diseases. It again will leach into the tank and kill corals. Once copper has been used in a tank, it should never be used to house coral.
Be very careful of what you pull from the local waters. Rock, dirt, wood, etc. It may be fine for fish, but again may leach unknown chemicals into the tank and kill any future coral.
Basically, if you plan to have corals in the tank at all, ever, don’t put anything in there that isn’t coral approved, sanitized, approved for saltwater aquariums, etc.
Blue crabs will kill the fish. They don’t go together. You get one or the other. Doesn’t matter what fish, the blue crab will eventually get it.
Get a Quarantine tank. Doesn’t need to be large, but anything going in the large tank should first go in the quarantine tank.
Reverse Osmosis water will be your friend and help minimize contamination, disease, pests.
Done right, saltwater tanks can be a blast and once dialed in, low maintenance, but takes a lot to get there.
Reefcentral was my best resource when I had my 200gal reef. The local guys may be great, but understand they are there to make money and there is no way one person can know everything about the whole aquarium trade.
You have about 2 years of reading ahead of you on Reefcentral.