I would hold fire on making a decision yet - EV1 are due to release a load of new servers around the 10th of next month, they will also revert to a $1 set-up - but they may also have some new models (I reckon they will be RH9).
You also need to consider things like support costs - are you going to be able to maintain everything, or will you need some sort of support.
Memory is always good - can these models be expanded by adding more memory if you decide you need it in a few months? I would opt for the 1GB options.
Just one correction on your IP's - you can have an additional 7 IP's with EV1 for no additional cost.
A good place to get ideas is
www.webhostingtalk.com - but like anything you will find fans of all three companies, and others that hate them. Also check out the forums of the companies - do they offer help easily - are customers moaning about issues etc.
Just a few thoughts - good luck in your expansion.
at the moment - but expanding all the time....) 
