Sounds like a great trip. We started out with a 10' popup and a minivan as well. My only concern with a family of 5 and a trip that long would be the lack of storage and fridge size, constant set-up and take down, and minimal access to things in tt while on the road.
Have you considered purchasing a used motorhome and then re-selling it when you are done? More space and comfort while on the road and access to a bathroom. Kids can move around a bit and you'll have much more storage room. You can still use the kitchen while on the road and safe a ton on food costs.
It would likely cost less than the $10k you plan to invest. You could always buy the popup later.
