You don't need Cisco Prime to iWAN.
iWAN is actually a collection of technologies.
For the crypto you will need a SEC or HSEC licence (HSEC removes the US export crypto performance limit, and greatly increases number of tunnels you can support). I personally prefer to use IKEv2 these days.
Next, lets assume you are doing site to site VPNs with a hub and many spokes. You'll be using an DMVPN style system. You then need to decide on the routing protocol you will need. If you want to use BGP or EIGRP you are going to need the old "Data" licence (now called an AppX licence).
If you are only doing user to site vpns you probably only need SEC and HSEC.
Back to the hub with many spokes configuration. I personally like using the hub as an IOS CA server and issuing certificates to all the spokes. I personally like using EIGRP, but Cisco do have a guide using BGP.
Here is one Cisco Validated Design:
http://www.cisco.com/c/en/us/solutions/enterprise/design-zone-branch-wan/index.html
Here is another good guide using BGP peer groups:
http://docwiki.cisco.com/wiki/PfR3:Solutions:IWAN