Can I have wpa and wpa2 on the same SSID available for both kind of users?
As mentioned already running 2 security postures on the same SSID can cause issues with connectivity. I tested this over a year ago and i discovered older clients (intel 2200s) and others struggled at times during roaming and associations.
While you can enable both it is preferred to select only 1 of them, but if you choose to have both enabled I reccomend that you configure them as follows:
WPA - TKIP Only
WPA2 - AES Only