4 kids I would go a Cruiseota for sure.......................... If you haven't finalised your order on the van yet I would stipulate panels and batteries now so that the final build weight has those things like batteries,panel, awnings etc all included in the original weight calculations, save a pain in the bum later on.
Even with a Cruiser I would keep the ATM no more than 3.2t all up, no sense in dragging a lot of weight around behind, anymore can also mean you will want to shell out more money for spring upgrade which is an expensive exercise for something that may be needed for a short time each year.
If doing off grid then batteries go for AGM, 105ah a minimum, at least 2 with 300w or more of solar if mostly parks then just a single 120ah with 200w would be enough to cover for the odd creekside camp, remember each battery will add around 30kg unless you have a fat wallet then Lithium is lighter but costs a heap and requires special charge regime.
Have a browse on here there are plenty of threads with great ideas on how to spend your money and some very informative threads on solar and batteries that will make your eyes bleed..........................
Most important anything to do with your van order ensure it is all on paper in the contract and intialled, do not take anyones word that it will be done, if not on paper it won't happen............ On Van pick up allow a few hours to check everything works, turn on fridge, open every draw and window/vent do not accept until very happy, otherwise they will tell you to check it out at home and bring it back, they will fix at first service 3 or 4 mths down the track, leave it in their yard till fixed, will make life happier for you...................
So welcome to the group, ask away about anything and don't be afraid to chime in, we sometimes wander a bit off track (usually the Victorians) but often after the main points are covered.......