I'm going to connect my panels in either 5 arrays, each being 2 panels in series or 3 arrays of 3 in series or 4 arrays of (2s/2p)

what are you using to measure each arrays V and Amp? (thinking something i can connect onto a Rpi to be able to push the values onto a MQTT subject to log and graph it)

G

 

You would need to measure both the volts and ampere individually. The two major hurdles you're going to face is that the Raspberry doesn't have an ADC so you need to use something like an MCP3208. And since all 5 strings come together they'll have the same voltage at the end. To overcome this you would need to put a reverse blocking diode on each string, that can handle upto at least +25% of the panels Voc and Icc values. Then yuo can safely monitor each's string voltages. For ampere you would need a shunt on each string. A 12a current shunt should do the trick. 

 

It's a hell of a lot of wiring and components, hence why the commercial string monitors are so expensive.