Casablanca Car

Ok, so in another question (that only got one answer) he said I should not build a box unless I know the spec.s of my speakers... ok...so what specks do I need to know... I have the names of them (well except 3 of the seven, but there just 2 5 inch mids and a bullet horn (tweeter), but the other 4 speakers I would put it in I know most of the spec.s... I have 2 8 inch MTX road thunder's that I am using as my rear speakers, and (I dont know the exact spec.s but most everythign is right on the back of the speaker) but I also have 2 subs... and thats makes 7 speakers all total.
I planed on making a symetricl box for them, and having 3 chambers in the back, one in the middle for the subs, and one on each side the the mids... so what else do I need to know?