I'm not quite done yet, but I figured I'd answer what questions I could.
1) Did crowdfunding work to enable you to complete and sell your deck?
Yep--more specifically, it enabled the deck to be (nearly) finished in a year-and-a-half, rather than another 5-10 years through self-funding.
2) How much of your deck had you already completed when you started the crowdfunding process?
17 of 42 cards (majors, Court, and Aces).
3) Were there challenges or problems in the process?
Getting the word out, and having regular updates to keep momentum going.
4) Which crowdfunding site did you use and would you use it again?
Kickstarter and yes--lots of name recognition, and the "all or nothing" model engenders a bit more trust from backers, IMO.
5) What methods did you use to let people know about your project and where they could go to contribute to the crowdfunding?
I bought a paid account and posted here, for one.

I'd also been attending a couple local conventions and showing finished pieces in their art shows. I also looked for other tarot and steampunk venues to help spread the word. I even experimented with Facebook ads. Over a few years I built up a small audience, so when the project launched I had some help getting the word out.
6) What advice would you give to someone about to start the crowdfunding process for their deck?
First, don't rush--try and build up some buzz about your deck before you ask for money. Second, and related, get some of the deck done before you ask for money--unless you're working with a famous IP, or have some reason for people to know who you are, you're essentially a stranger asking for money--the more you can show folks exactly what they're backing (and that you're serious enough to put your own time and money into it before asking for theirs), the better your chances are, IMO.
Good luck!