Hi 

A few ideas to start. Look at the threads here where people discuss what they use, and some people have put lists of power usage for their items like fridge, TV, pumps etc. 

If you have a three way fridge then you should only use the gas while you are stopped. The 12V power usage is normally too big for running off batteries and is not regulated so continuous high current draw. You should only use 12V while the engine is running and have an automatic cutoff when the engine stops to prevent flat batteries. 

Your car alternator is a potential big charger for any house batteries. It will charge the batteries while you drive and can be used for emergency charging in poor weather also. Look at how to achieve that. Modern vehicles with a 'smart' variable voltage alternator will normally require a DC-DC charger to work properly, older types may be easier to setup. Note large connecting cables are needed and probably anderson plugs to connect them between the van and the car. 

Without running a fridge on 12V, possibly one good size battery might be Ok. More is better. Portable panels are OK and handy in some circumstances to chase the sun when power is needed. Roof top panels are just easier. Put as many on as you can fit is my suggestion. You need a regulator and should get at least a three stage unit with settings that can be changed to get good life out of the battery. The ones supplied on portable panels are usually poor quality and really should be mounted at the battery to work well. All wiring should be done with generous sized wiring to minimise power wastage on resistance. The small extra cost of better wire is only  spent once.   

There are some good books by Colyn Rivers available from libraries or for purchase from a lot of places that will give you all the information you need. I have a couple.

https://rvbooks.com.au/collyn-rivers/

Cheers Jaahn