in most cases yes a single box will do, for most home users,
the next thing you want to think about is storage space,
file shareing & FTP plus a Web server can take a lot of space and can get in to a lot of $$$$ when you look at high end stuff, but again for home use 200 GB or so should be enough (This realy depends on how much data you will have etc... example a DVD format movie can take 4-7 GB each). and if the data is high value (i.e. if can not be lost) then you will need to dubble that 200 GB bacause the drives will need to be mirrored etc...)
you can look at 2 diffrent type of Drive's
IDE = cheap in price, good preformance, but limited thru put etc...
SCSI = $$$ very High speed, High preformance Raid, Fiber bus etc.....
Next thing
who will be accessing the Server ? just home users, Samll group of people (10-15) or open to the public,
2 things here... Security & Bandwidth both cost $$$$$$$
the problem is you may need them both in most casees you will run in to both issues at some point.
I think you can see from this it takes a lot of thought to do it right,
the list can go on & on but just think about your want to do with it
in general for a public web server / FTP server
the following things play major parts in the sizeing of the box
Type & amount of Data
Number of users
how fast do you wnat the data to move (Bandwidth)
Viideo & audio become less of an issue as it not a factor for the output.
