Leave the grain bill the way it is and see where you end up.
Make sure your your measurements are accurate so you know exactly how much water you added and how much wort you ended up with. It helps to know this to determine your efficiency along with boil off rate and grain absorption. Try to figure these figures out so you can adjust the volumes next time if you need to. Do some research if you don't know what I'm talking about.
Test your mash temp every fifteen minutes and crank a little heat if you need to in order to maintain a steady temp. That's what I do for BIAB. Odds are you Ph is fine but if you wanna buy some testing strips you can.
Most of all have fun and don't stress if it isn't perfect.
I think it's great NB is offering these kits. 3 gallon BIAB is a nice sweet spot for brewing indoors while still getting a decent amount of beer. Plus with time savings of BIAB you can brew more often, in the evenings, etc.