With some coaching from JennyP, I ended up making it like an envelope. The tablet slips in the pouch and the flap folds over. I put felt on the front and the little flap has velcro.
I also put velcro on the back of the tablet and the little pen holder so they stick to the felt. On the inside of the pouch is a piece of bookboard, so it becomes a lap pad when I'm using it on the couch. I'm really proud of the little handle. It looks really cute!