Which one first?

[Putter]

I would go with the bags first. Then you can accurately determine if the diameter wheels you want will fit. I am not sure, but I think the only real difference in f/b and f/b/s/s is the number of valves and switches/relays. For f/b, you really only need two (one for the front and one for the back), but for f/b/s/s, you will need one for each bag (4). And a few more switches and relays. Go ahead and get the f/b/s/s. You may as well spend a little extra now and have it all, rather than deciding you SHOULD HAVE done it and be forced to reconfigure it and spend more later. But that's just me.