You’ll have your chassis battery for starting the motor etc. I’d suggest leaving that alone. You don’t want to get stranded.
Consider adding a house battery. That would be a 12v deep cycle battery. Both batteries can be charged by the van’s alternator. Make sure to separate the batteries using an isolator or battery separator.
If you are on the move daily then you could get by without a separate charging system for the house battery.
The house battery by itself will run your 12v Interior lights. Add an inverter to run your TV & Kids playstation.
The microwave will consume a lot of power if you use an inverter. Allow for 100 amp current draw (or more). The cabling from the battery to the inverter should be as short as possible and the right gauge to handle that current without a drop in voltage.
A quiet generator would also run the 110v items. I say quiet because most campgrounds have rules re: noise. Most campgrounds prohibit you from running a generator past a certain hour.
Check out all of Terry’s photo’s of one of his custom conversions:
The photos can take a while to load depending on your internet connection but are worth the wait. There are closeups of his converter (converts 110v to 12V and also charges the house battery) and his battery separator etc. It’s like a "how to" manual!