When I make my bags, I usually iron a soft fleece or interfacing to the outside layer of the bag. I almost never use interfacing on the lining. Look at it this way...it's your "art', who's to say what's right or wrong?
I bought some of that fabric last week. It was on sale already for 40% off. I purchased enough to make two little toddler dresses, but I'm wondering what should I do with the excess that I have to chop off for them. Any suggestions?