IMHO you need way more working capital than 15K... heck Im almost at 5K on my RSR XL200.
Before you do anything, get your business permits, and location where you plan to propagate all locked down... no clue how you can figure everything else out until you build this foundation first... till then, you're a drunkin reefer with a pipe dream! Sounds like you'd be better off working in your basement, and having this as a side hustle.
Also.... live sand... really? You would be out competed by the name brands out there, and other LFS. As far as Live Rock.. once again, this seems to be a fail, as most setups these days are following a dry rock start up method, with far cheaper costs.