Ok, I've read a bunch, but want to to get opinions anyway:

Battery and cca.....battery is a DURACELL SLI24MDC, (GP24) CCA 500, MCA @ 32° 615 ....I know to add a second battery to mirror the specs on the first battery, (brand name is probably irrelevant, although I will probably do same/same), is this enough battery to add another the same or should I go more?

Never used a Duracell, like to have Interstate, but won't waste money if brand is irrelevant.

6 gauge.....good to use?

I will install an inverter in the future, but, don't know what brand of Inverter or how to figure what size inverter and a wire diagram....I am capable of doing the work, just need a schematic or diagram to follow. I have been googling a lot.

Thanks all.
Ray