I personally would not consider hosting this on shared hosting, given the scale of what you are planning and the need for absolute security, but of-course the decision is yours to make.
Also, considering the (relatively) recent changes to United States law related to online gambling, you might want to consider a hosting company outside of the United States.
You might be interested to know that the DreamHost TOS explicitly prohibits a customer from maintaining more than one hosting plan. I have no idea if they actually enforce this clause of the TOS, but it is worth knowing about…
[color=#0000CC]“The Customer agrees to hold only one (1) active web hosting service plan at any given time with DreamHost Web Hosting. Signing up for multiple plans is grounds for termination of all additional plans without warning.”[/color]
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