Those resistors are supposed to be mounted flat onto a metal enclosure (preferably with a blob of thermal compound in between) if you want them to handle 200W continuously. Stacked up like this, they're going to heat up reasonably quickly.
Have you done any thermal calculations on these?
Personally, I'd put the binding posts below the LCD, because otherwise cables are going to be obstructing the view of the display.
Not aware of any existing modules that would suit your purpose.
The simplest solution I can think of is a RMS to DC converter (
AD, for example) and then a microcontroller for interpreting the results and doing calibration.
Another solution would be to put an audio ADC in there and process the samples with something like a Cortex M4. This approach would be more involved and require some DSP knowledge.