I am no expert so my reply will be overshadowed by better knowledge.
However, I have a 3640 which is a basically a chassis that can take a set of network modules. I am sure that there are a whole range of chassis available.
The next thing is to ensure that when you purchase your modules you get the correct version of IOS. I had fun with a couple of Fast Ethernet modules and a version of IOS that couldn't see them. The version I got in the end was LOWER in release number. Quite spooky really,
Regards,
Sam.