an llC is only for liability protection, being a single member LLC will have no effect on your taxes.
having a business plan is important they contain the steps you'll take to make it profitable. many startup businesses lose money the first couple of years until they can build up their client base. take too long and if audited, the IRS could argue you are engaged in hobby and disallow any net losses.
if you know little or nothing about boat chartering, get advice. certainly there may be state or local licensing requirements, can't say if your boat will need to undergo coast guard inspection, if you have crew, you may have payroll tax filing requirements.
you may want to read this
https://www.allatsea.net/chartering-your-boat-for-fun-and-profit/
