im told a full 47 slot server uses 2MB upload a second but that VERY rarely happens. I also worked out roughly if you have, say a 300GB bandwith limit every month, you will be able to host a LFS server full for 12-14 days Constantly before you run out of bandwith.
The best thing to do is to use the LFS ingame calculator as it will help you a lot
Out of intrest, how much bandwith you have to play with?