If you are going to be using a sub, then most definitely keep the midbass units at 6.5" or less, preferably in the 5-6" range. The upper midrange response is vastly better than an 8" will ever have, and you don't need the drivers to go that low in the bass. If you want a specific recommendation, use the Vifa 13WQ, it is a classic and still one of the best midbass units out there. Look up the Ariel by Lynn Olsen (I can't recall the website), it is one of the best uses of this driver and has a ton of info and support. Even if you don't end up doing this exact kit, it is still a good way to start your education.
