Hi,
If i have this type of server
Celeron 1G
1G RAM

Then i will place there 8 reseller accounts with
5G space
50G bandwidth

Then they are using the max 50G bandwidth in a month all of them.

The question is, do you think the server can still handle this?

Totally depends upon the type of sites they host - Static html pages you could host a couple of hundred or more on that server but just a few database or cgi intensive sites could cause problems - you might need to limit their resources or services - Only allow a fixed number of db's etc.....

Bit hard to say that the server can handle what you don't know is going to be hosted on it.......