For me to host this website i would budget it around £3400 per year for first year, this includes the price of the dedicated server.
I'd say £2500 a year.
Let's not forget that the "users online" is a 5 minute average synoptic of useage. That is to say; there might only be 5 requests at any one time going to the host machine.
The main issue would probably be uplink speed; above 1Mbp/s at least. (Iv'e known pentium 200Mhz systems do really well on a T3 uplink, as servers) The other issue is physical memory.
All very complex stuff.....but this is what you get when you work with computers
Wf.