Welcome to your new addiction!

Okay, let's get the whole horse-and-cart thing in the right order.

BEFORE you put any money down or start worrying about the FAA, ask yourself what the mission of the aircraft will be. Too much aircraft means too much money/time, while too little will mean you won't be happy once it's buil....

Scratch that. Before you get serious, check your spouse/significant other. The reason homebuilts are less expensive (in most cases) to production aircraft is that you're the labor, and labor is a huge cost in manufacturing. It's an investment in time and money that has to be fenced off for the project from other things. Forget airplane widows - they have it easy over airplane widows most of the time if it's not handled properly.

Be realistic about the money. The kit/materials are the starting point. There are tools to be purchased - one doesn't need a whole machine shop, but one does need an assortment of power and hand tools. And a place to build and store the thing during construction.

"Um, honey, for the next two years you'll be parking in the driveway while I build an airplane in the garage" is not a conversation to have after the crates of aluminum and stuff arrive.

Shop EAA chapters in your area if you can. Each has its own flavor and experience! I got super lucky in that mine matches my needs in what to learn (everything) and attitude (if one is building a replica Starship One or a weight shifting trike they're both really cool airplanes and worthy of attention). Forget all the junk you'll read about the National Headquarters on the forums here - the EAA is the local chapter.

I would suggest NOT buying someone else's project. The threat of having to repair other people's fixes is a real danger to time and money. It is actually easier to rebuild a part than to fix a botched one.