Alas, you've strayed into territory that is rife for disagreements. There is no single "good" answer to this question. Were I the technical sales person for your account, I would first look at your existing infrastructure. After all, would I recommend Oracle to you if you already had an AS/400 in house?
I would also ask the modules you are plan on running, as some modules (such as Sales Order) are more processing intensive than others (like generic Financials).
Another consideration would be the volume of data you would be migrating from your existing system, for surely you would like to be able to look through prior year activity.
A few other questions to ask: How much customization needs to be done (custom reports, modified functionality, etc.) outside of the initial data conversions? Disaster Recovery preparations? Is there a need for remote access to either the regular web client, or for developers? What is the daily duty cycle (24x7, 5x8, etc.)? Are there external interfaces that must be accommodated to feed/accept data from 3rd party systems?
In our company, I know we would ask these questions, and only after looking at your application requirements and growth pattern would we start sizing the hardware. Gregg Larkin's quote used to be something like "Remember, you're unique, just like everyone else." (Apologies to Gregg if I got that wrong.) With your question, this is especially true. I would not give you any recommendations without knowing more of what your particular needs are.
Sorry to answer a question with more questions, but that's the nature of this beast.
