I read the other posts, but I think what you're asking is not about bug in but what else you may be missing?

I'm also a big bug in proponent, I want to stay with all my stuff and, if can't, rely on whatever fraction of gear that I could successfully haul in worst case scenarios.

So you have the major stuff covered, it sounds like.

As far as your chair- do you have grade aids in case of hills that you could leave in the van and add on in a pinch?
Are you top heavy or could you sling a pack over the push handles without a tipping hazard? I'm sure you know anti tippers can be a hassle even on curb cuts and such.
If not, is there enough space on your lower front to handle extra gear? Like maybe a small, wide board to set and place your feet on that could extend past your toes and become your haul platform.
Are your front casters air filled or meant only for hard surface? You may want to get some quick release 3 or 5 inch inflatables for easier rough rides.
I'd avoid flat free inserts, very stiff, and go with a commercial bicycle anti puncture treatment, Mr Tuffy, Slime, etc. You could do that with your vehicle tires as well, I think.
Also, if you're in NE Ohio, Invacare is based in Elyria, see if you can become a product tester and score some free stuff. They used to manufacture some Quickie knock off's that were very reliable. I think they sold that division but may still have product.

If your concerns are vehicle based only, forgive my digression. I don't know what you've considered in case you have to push sans van for any length of time.