General RV Solar Questions?

I'm planning to add a couple of new high end Kyocera 140 panels and build up a new system out of them. Currenly I have what my old 95' Squire 400 came with which is a substandard and smaller panel with an ACS Specialty Concepts Controller. This unit has one red light and no digital readout. It does keep the single 12V house batt charged and that according to Lances typical (and also probably substandard) idiot light array monitor.

I have no experience on solar but have been researching for a year or so and doing a lot of reading and on line window shopping. My thoughts are to begin the learning process by adding a better charge controller and an inverter since there does not seem to be one now.

I am aware that panels must be matched but I an considering (roof space allowing) leaving the existing system for "house" use and adding the new system with a huge inverter and of course components to match.

That being said, I need to determine the power coming from the existing charger before doing anything. Is this correct?
Also, how exactly can I do that to get a legit reading?
I assume I can get a reading in the fuse panel where the lines from the existing controller enter. Is this correct? I have a good meter so this should not be a ploblem, just correct procedure to get started?

Any assistance greatly appreciated. Morgan