I have a similar system controlled by a PLC. My first brew on it I was similar to you--ended up running my 4500W BK element at 70% boiling 12-13 gallons. I throw in an additional 2000W heatstick during initial heating, but pull it out when it gets close to boiling. I have a HERMS coil in my HLT that rests somewhat on its 5500W element, like your BK IC situation. No issues so far, but long term, I don't think you want too much lateral pressure on the element. Probably need to consider legs to support from below or some way to hang it from the top. I also have a similar set up for the mash and sparge water. I use Promash to calculate water needed and batch sparge. Ended up with an extra gallon into the BK after the last brew, so I have some tweaking to do on the numbers. Overall, your approach sounds pretty typical.