RAP-3s ship with IAP SW on them. As such they can be a VC or you can have multiple RAP-3s in one group. Remember, for multiple IAPs to form one group the management traffic must be in the same Vlan. No external controller is needed.
The RAP-3 does support 3G/4G. The card we support in the current release (v.3.2) is the Verizon Pantech UML 290. Make sure you are running v.3.2 as there was an issue with the UML 290 in v.3.1.
On a side note, v.3.3 should be posted to the support site in another week or so.