I say, since they'll be hard to make, put em off until all your other stuff is done :'D
Then just use an old pair of slipons and hotglue. if you glue anything near the bottom and are scared of it coming off (lol my foam) use rubber cement, since the edges near the bottom usually are rubber and hotglue doen't stick so well to it ._.;
EDIT: OH WAIT I keep forgetting sora has zippers on his shoes. Like... first sew a strip of fabric-zipper-fabric that'd fit on it near exactly, and hotglue it on oux well, that's what I'd do.
EDIT2: what board am I in O-o;