Try using Cisco Config maker, it is a Cisco free program to help configuring your routers, and it well help you on understanding what options you have and how to configure it, it can even configure the router for you.
Your Bandwidth is low, f each user would download at 3KBps that would be 24 Kbps, meaning that 10 Users would fill up your 256Kbps.
You do need a Proxy, with at least 2GB of disk space to balance your users requist and cache most of the accessed pages.
Use a proxy that would increase your bandwidth not lesss than 40%
Good Luck