I don't know what the specs are on any of those machines, but that sounds like a descent setup to me. It does look like you are getting pretty close to needing another APE though. Below are a couple of links that can help with sizing, APE licensing, etc.
Multi-module system guidelines
Maximum capacity of SolarWinds infrastructure - SolarWinds Worldwide, LLC. Help and Support
Loop1 Systems: SolarWinds Training and Professional Services