David,
1. The recommended version of software for the WM3600 is it's final software release, WM3600-5.5.5.0-018R.img.
2. The AP4600 and AP4700 are supported on this version.
3. Other supported models include AP4021, AP4022, AP4511, AP4521, AP4522, and AP4532. AP3500 series APs are NOT supported.
For full release information check the release notes which can be found on the
Support Portal.