Alas, yet another cry for help today!

I'm just starting to book weddings and I'm trying to work out all the details and kinks. Right now I charge a $50 non-refundable deposit to book the date. After that I tell my brides that everything else is due 30 days before their date, when we finalize the design and number of servings. I realize this might be a bit far out but 30 days is what it is right now.

Here are my questions:
I'd like to have some sort of a payment schedule so that I don't have them cancel 45 days before their wedding and I only have their $50 left, especially if I had to turn down another wedding after I booked theirs. I'd like to do a percentage of their total for their deposit, and collect the rest of their payments on some sort of schedule. The problem is that only a couple of my brides have ever had an exact idea of what they want their cake to look like and they frequently have only a vague number of servings they want. How do I work this out and what kind of payment/refund for cancellation schedule should I work on?

Thanks so much for all the invaluable advice. I appreciate it so so much!

Charge a 50% non-refundable deposit.

I've also seen some people do a 30%-30%-40% payment schedule, with the last payment due three weeks out or thereabouts. There were different refund policies for each payment if they did cancel, something like "no refunds on payments received more than a month prior to the date."

I do 25% non-refundable for any reason retainer, remainder due 21 days prior.

If the bride doesn't have an exact number of servings or style, do you just estimate?

At the consultation, we have to have an estimated number. I generally use 75% of invited. And during the consultation, I make sketches and the bride picks the cake design.

When I was getting married(2004), I had to put down 50% of the total price of the cake as a deposit and to hold the date. I HAD to have an estimated count of people (the final count was required one month before), and the design down.
The remainder of the total amount, was due two weeks before the wedding date. I'm pretty sure that's what it was. That's what I'm going to do once I get into the wedding cake business part.