Re: seating question
I'm not Baja (nor do I have his huge knowledge base!), but having just been through a process of learning about pre-tensioners, etc., I can offer up what I do know.
First of all, different generations of vans have different details on the airbag system. But I think they all incorporate seatbelt pre-tensioners. This is the chicken wing shaped bulgy thing that is just below the female receiver where you "click" the seatbelt into. This is a pyrotechnic cylinder/mechanism that pulls the seatbelt tight if you have an airbag deployment. It is keyed to your van and your airbag system, so you want to keep it with your van.
The female receiver and the pyrotechnic gear make up the pre-tensioner, and you will want to mount them on whatever seat/base you end up with. You can look at what you have now to see how they have handled it. My post-SMB rig came with aftermarket seats on Ford bases (Flexsteel seats) and they still mounted the pre-tensioner to the seat/base, just like if I had stock seats.
If you don't have the pre-tensioners there and wired up, your airbag system won't work (and will flash codes at you). It is possible (at least on my generation) to get around this, but I can't see why you would want to (I wanted the option to remove passenger seat and still have airbag system as a whole be functional, hence why I delved into it). There is more info and some photos in a thread called something like "can I just remove the passenger seat?" that I started.