Not sure I'd like to have DPF. I wonder how often it will have to go through its burn cycle with Euro 2 fuel.. On the flip side, with the DPF particulates will be zero. No fears even if ASBU's are resurrected.
Re: rear coil springs they should be fine if you stick to the maximum load capacity. I don't see any issue with coils if they are rated with the same capacity as leaf springs. Coils are also easier to change out and cheaper compared to a complete leaf pack. And yep, airbags are awesome. You can soften/harden the suspension any way you want depending on your load. Just a bit expensive.