Simon 5 is coming soon!
Simon version 5 is currently in beta testing. It is a massive update, introducing a much-requested feature: syncing the Simon data between multiple Macs, plus a Simon Status service, a Link Checker filter, improved Find filter, iMessage and Speak Error notifiers, a new app icon, and much more.
Important: please note that Simon 5 requires a minimum of macOS 10.12 (Sierra), and will be a paid upgrade from Simon 4 after the beta. Purchasers since September 1, 2020 automatically get a version 5 license (that also works in previous versions).
Re: Using Proxies with Simon
That isn't something I've had experience with... but Simon's web service works just like a web browser, so any proxy settings in the Network System Preferences would apply.
You could also make a custom script to access a website via a proxy; something like this:
curl -x {Proxy Host}:{Proxy Port} {URL}
The curly braces are custom variables, which will show up as fields in the Test editor.