We currently have 5 4400 series WLAN controllers deployed throughout a school district and want to upgrade to the 5500 series. I'm not sure what the best practices are but could we deploy a single 5500 series controller in one location to replace all of the 4400's?
Each site is has either a 100mb or 1gb Metro Ethernet connection depending on the size of the school. Can we install just one 5500 and manage all access points across the WAN or do we need one at each site? We currently only have 150 access points but are planning on growth in the future.
This is mostly dependent on your traffic flow. If all of your servers and Internet are located at your central site, there's almost no reason to have your controllers out at your remote sites. However, if those kinds of resources are located remotely, you should leave controllers out there.
I've implemented both kinds of designs, and both are fine. Placing a smaller controller at each remote location and a couple larger ones at the central site provides plenty of redundancy. The 5508 also provides 8 uplinks, each 1Gig, providing more redundancy at the site itself.
Your bandwidth isn't a concern at all, and the 5508 can support up to 250 access points. I think you have a good environment to deploy only central controllers, again as long as your traffic heads to your central site for most applications anyway. It's certainly very helpful to have only a couple controllers, rather than 5 or more to manage.
In the end, there isn't a major difference in designs between 4400s and 5500s.