Because I just whip stitch the covered foam core bottom into the bag, I can remove it to launder. I found some woven nylon stuff at wallmart on their $1 table a couple of years ago. It looks very sheer, but is really strong. I've been making my inside pockets out of that (I bought the bolt) and helps keep the weight down. I will cry when my supply is gone. You might want to look at ripstop nylon for the lining and inner pockets. really strong, but light. I would also guess that purse feet are going to be lighter weight than the rubber feet and fasteners.
My purse weighs a ton because I have to carry stuff that my husband maybe might need someday: 'here put this broken screwdriver in your purse, we might go to Sears someday...', 'what do you mean you only have a 3' tape measure in your purse?', etc.
The bag really sounds fabulous, Please post a picture!