I built mine the same way your planning except I didn't go the HERMS route. I didn't find I needed to. The only thing I have a hard time with is mash out but that doesn't bother me. I normally get around 80% brewhouse efficiency sometimes as high as low 90's.
I recommend not cutting out the tops of your kegs but flip them over and cut out the bottom. The the tops of the snake kegs where the spear goes is actually fits a 2" tri-clamp. Doing it this way you can drain every last drop from your mash tun and makes clean up a breeze. Also you can use the bottom you just cut out just drill a series of holes in it and you've got yourself a false bottom.
The control panel doesn't need to be anywhere near as complicated as you see on other electric breweries. I found that all the lights and alarms might look cool. But not necessary at all. My panel is very simple it has a PID, on/off switch, thermocouple and a plug for either HLT or kettle. There's no reason for me to keep the HLT hot while I'm boiling so I just plug in whichever vessel I need to heat.
This is how I did it anyways. I hope this helps a bit. Good luck with your project! Hopefully you find it as fulfilling as I did.
