That dealer sounds a little sketchy. I understand the desire to get to the front of the list, but you're asking to pay more by putting down a deposit this early. Allow me to explain.
First, you go to the dealer committing to a car you haven't test driven. This shows the dealer that you will get this car no matter what obstacles are in your way. Thus, you put the ball in the dealer's court.
Second, by offering to pay for a spot before knowing the price, you suggest that you don't care what the price is. The dealer can ask for a deposit without guaranteeing that you will pay MSRP or less. You could be paying MSRP plus your deposit for all you know.
Third, by discussing other deposits with you, the dealer is gauging your interest. You don't know their deposits, and I bet that you will want to be on that list to guarantee a spot. You will be willing to give them more money to get your spot. They may even offer to place you higher if you give them more dough. The dealer may raise the deposit to commit you to the sale. This brings in a solid commission for the salesperson and gives the salesperson the opportunity to lower customer service standards with you. You're committed to the car, not the dealer, and the dealer knows this. Because they know this, you may pay more, get treated worse, and not get the same deal as someone who cares more about which dealer sells them the car.
I would definitely get something about price written and signed by the dealer. If you can't get a written guarantee of MSRP, then I would talk to another dealer.