Hi,
The process involves two steps..
1- Open Google wallet account.. this is another name for a merchant account where you can accept credit card payments.
It is during this point that you need to pay the $25. Google said they are not interested in the $25 dollars, but they just want to distinguish the serious people for those who are not
(I wish I could distinguish a million good people this way).
2- After you setup your wallet, then go to the developer console and open a dev account, and since gmail, wallet and dev con are all belong to google hen they will know you have a wallet and the second process will be much easier.
It is ok to use existing gemail.. it really doesn't make difference.