Wish I could give a well informed comment!
I only lace the back and lately have been very slack () and have even used craft glue in a hurry to get a gift framed!
I've never used sticky backed mounting boards, but my American born friend has, she's back in the States atm, and she loves them! Especially for smaller projects. It's not so avaiable in Aust.
I don't usually use matting as it's not readily available, as well as matt cutters in our craft shops. So my projects don't have matting boards, which I think they would look even better with them, but well, that's the way it is.
Don't think you could use padding unless the frame is deeper than normal. As once you've got the stiff cardboard to mount the stitching on, then your stitching and you try to get that to fit in the frame, I don't think there's room for anything else!
Sorry this isn't going to be much help, hopefully someone with experience can comment!!??