If your hunting for Perfects its more efficient just to go hunting for one, but best way to make money quick is to have a team of 6 armado using the hoarder trait to pick up items after battle. Escape flashes sell at 2000 a piece so it'll take 2000 of those alone, but you can also sell off the extra spinners cakes and scents they pick up to. It never gives you the option to use the Coupons, so no on that one.

I did. On my second playthrough I was using a whole team of patterbits for the campaign - maxed out the robber trait on each one, and each of the battles against other tamers was starting to yield 100,000s of gold per battle towards the end. As far as the coupon goes...honestly I can't even remember if I remembered to use a coupon or not haha.

you cant use a coupon after buying it, honestly not really worth all that money