Well done on this simple design , about 12 years ago i had built 3 or four using similar design but rolling bodies from 253ma steel as its a bit more heat resistant. Slightly different way of firing the system up, but still drip feed. Used standard diesel burner controller , this was to fit within Erma's and HSNO policy here in NZ for combustion equipment. This was then coupled up to a standard chemical dose pump with 4 to 20mA feedback from a thermocouple in the burn chamber. This modulated heat output rather well because of different grades of waste oil Because the units I built were going in glass houses we required control both to keep the client happy and the clients insurers. Some form of flame monitoring would be good, here in NZ it is a requirement if used within or near building could be adapted easily to loop into your time. I mention this because back in the 2005 period there was a trend with the glasshouse growers to use Kroll and there had been a few fires caused by over fuelling, looks like you're on the right path, well done. I never continued as we started battling the boffins and all the rules and reg's . Even did exhaust gas analysis which turned out really good, however because of the ash in the gas it was recommended if you have rainwater for drinking not to use one within 100m of the collection area as some waste oils ash is very toxic , contains high levels of chrome, copper, zinc, and a few other surprises when we had it tested . Your burning the worn bits of someone's engine . Well done, Jayson.
However nowdays the worn bits of the engine, are left in the filter, we use before burning.
Also we don't get ash exiting the flue so I would think any nasties are cremated in the pot, and we only use gloves when dealing with that stuff.
More information on the burning of waste oil is available in this EPA Report. Quite interesting