Hey Sebastiaan,
I would say it depends on your traffic flows and enviroment, how u would like to design your Network. The 5508 is able to handle up 500 access points for business-critical wireless services at locations of all size. 16MB per AP (theoreticaly). When u think to HA, normaly not more than 250 AP's will join one Controller.
how much want u deploy? the 8 Gbit could be a limitations but I would say u can use the local mode if you want.
much more relaxed will be H-Reap if your desing allows that.
We use a mix mode, depends on the SSID.
regards,
Sebastian