You probably have ethernet. So:
100 Mb/s ~ 100/10 MB/s = 10 MB/s = 10000 kB/s
The maximum upload you can get is this. With a slot of 4 kB/s:
10000 / 4 = 2500 clients.
I really don't know if there is a limit on the number of downloading clients. Well, anyway, do this:
- Change Download limit from 0 to 10000;
- Change Upload limit from 0 to 900;
- Change the slot allocation to give you the desired number of clients n = 900 / (Slot); With an ethernet connection, you have the opportunity to use a slot of something relatively big, like 10 kB/s, but that will give you "only"

90 clients at the same time. With 1 kB/s, you get 900.
And you will still have 100 kB/s to navegate with your browser.
Cheers!