$750.000 may sound as a lot, but it’s not that much for a new operation.
Are you counting in this budget the available cash flow reserve you need, since the credit card processors withhold the money for quit a while with new merchants?
Set up an affiliate program right away; however be careful with getting all of your new traffic from affiliates. You cannot allow more than 30% (max 40%) of players be tied with affiliates. Otherwise your profit margin will go drastically down, and after paying software, royalty and commissions you’ll be left with nothing.
Please consider developing CD campaigns, really strong sales team, and hire a customer retention manager!