1. I can't answer this one, as I haven't tried that combo yet. It sounds like a real winner, though.
2. I think that Opti-Seal gives a pretty comparable look to
UPGP. I really do like UPGP better, though, as it has among the best environmental protection of any of the sealants.
3. You would get better durability from the DWG (and any sealants you then put on top of the DWG) if you put it down on bare clear coat. Sealants (and DWG is a weak sealant) typically don't bond well to waxes or traditional glazes, like Red Moose. You mentioned that you did Vanilla Moose->RMG->Opti-Seal. The Opti-Seal isn't going to give you very good durability that way, as sealants won't bond well to traditional glazes like RMG. Try using the DWG instead of RMG. DWG is *meant* to be used prior to a sealant, so it won't hurt the durability/bonding of any sealant you put on after the DWG. RMG is great stuff, but if you're going to use it, you should top it with a carnauba based LSP. RMG plus a good carnauba will give you good defect hiding abilities if you need to cover stuff up.