John,
Welcome to the Hubitat Community. My son and I are the authors of ST_Anything / HubDuino. I think you will find it relatively straightforward to use your own DIY sensors, assuming the devices you currently use are already supported. If you can provide some more details of what you use MySensors for today, I can let you know how easy/difficult the conversion would be.
[Note: The Hubitat Engineering Team recently released a new feature to the platform that I am currently adding back into HubDuino. This will make the set up slightly more straightforward, if you can afford to wait a little while.]
