I think a bigger question is the design of the site and what sort of peak traffic you all expect to have to build for. I think it is unrealistic to have to limit yourself to one machine though and probably should be brought to the attention of whomever is in charge of your budget. Upon initial perusual of your existing site, there are a lot of images/animations that could / should be moved to a separate server to reduce load. I cant overstate the importance of design and testing to see if your planned implementation is upto the job.... good luck.
