I can measure the racks in my R Flow tomorrow night if you like.
If I was to tell ya a number tonight I would be just guessing. But I can tell ya that I put in plenty of shelf supports, right now I run a total of 4 shelves, 2 on each side. Perfect for brisket and butts.
I could add 2 more shelves to each side if I wanted to do ribs only. With a total of 8 racks I can cook 24 slabs of giant untrimed spares. Or 32 slabs of st louis style(trimmed).
I bet the hot rod deal is making you want to hurry but remember good things come to those who wait, sometimes.
Give it time man, get the rig just right. , get happy with it, have all the ins in place and......let the good times roll. That way its not a rush, and you will enjoy it alot more.