With an order of that I'd have 12 inches of leather for three handle and an addittional eighteen to twenty two inches of replacement leather to work with in case of a mishap and to make the top bind. I could also make a second strop just from the spare if everything went well although I've never gotten product from this vendor - so I'm not too sure it will 'tool' as well as he advertises.
I'd use the same material as the strop itself but become expensive to buy so much.