I JUST bought a Pearson 303, and am walking through my house, trying to figure things out. My BIG plasma screen, the giant speakers, etc. will go through Craigslist or whatever, along with a LOT of other stuff. I'd love to be able to avoid $100/month or whatever for a storage unit.
My plan is to be living aboard by the middle of October, but I may still be going back to the house to continue the clearing out process. It's a BIG change, but I'm committed and willing to do what it takes to make my dream come true. I like George Carlin's skit on "Stuff", and will keep reminding myself of what he said, as I go through this potentially painful process.
Expect to have a few weird moments during the transition. When I moved aboard years ago and as I was selling or giving away most of my belongings, I kept having this weird feeling like I was dying in some way. I guess it was the life I had known was dying. Just sayin', be prepared for that. Or maybe I'm just crazy. Anyway, once aboard, life was great so no problem.
As for the OP's storage question, it will vary from marina to marina. An old nearly dead van makes a perfect solution, there are several parked in my marina's parking lot that never move. Just wash it once in a while so it's not an eyesore. As for storing tools, try to find a place onboard for them if you can. Remember, "if anything's gonna happen, it's gonna happen out there".