Capacity planning for eduroam is no different than any other wireless infrastructure capacity planning exercise. We recommend consulting guidelines from your hardware and infrastructure provider.
For IP space planning, expect that your largest audience may carry on average 2-2.5 devices per person, each requiring an address. A single class C may not be sufficient. NATing to a private address space is recommended, provided it meets the eduroam logging requirements (you can back trace an IP & MAC address to an authentication).
Bandwidth throttling is to be avoided as best as possible to maintain sufficient quality of service for eduroam users.
Be Aware of Spectrum Interference & Density
This is not specific to eduroam but should be considered to avoiddegradation of your Wi-Fi service: When planning for burst network usage and high Wi-Fi usage from conferences or other large gatherings (e.g. sports venues), you may need to analyze spectrum usage, signal strength, and density or interference of Access Points at your site.