WELCOME TO AA!!
Please do not cycle your fish with live animals.
It's good to have you here and I think you will be pleased with the advice, personal experiences and knowledge the folks have here.
As for a water tes, I have the Saltwater Masters Test Kit, it is decent for a low price and tests the basics.
Websites, we have a general retailer section, you can read up on some, but lots of folks like
and there are a few others, those are the ones I have ordered from.
I'm not sure on the GPH
for an overflow, it probably depends on what you want to keep in your tank.
, some things you can buy cheap (very few) and others, (skimmers, heaters, phs) you should go for the better brands.