Race wheel newbie questions

With 60s you can buy tubes with valves up to 80 mm I believe, which is enough for these rims. they are a little more expensive. Some people use valve extenders, and there are threads (and even articles) here and elsewhere (ST) that describe how to use these and which valve stems you need. I honestly don't recall all of the details off hand. 

Enjoy the rims. I love them!!

Swapping cassettes is really easy.  Takes less than 5 minutes given the proper tools.  No skills required.

As far as extenders, if you have a FLO 60 and disc, my guess is that you can use a standard valve length tube on the disc and a small extender on the FLO60.  I like to use tubes that don't require removeable cores in this setup because I can use the same spare tube on either wheel simply by adding or removing the extender.  You do NOT want to be fiddling with removeable cores on the side of the road.

I used to run a covered training wheel with a Zipp 404 front, which as far as tube valves, is the same setup you have.  I would run latex tubes on both wheels, and the front wheel required a 32 mm extender to get it from 51 mm to 83 mm (use a little plumbers tape over the threading before attaching the extender to help the seal).  I would recommend at least 80 mm of valve stem length for your FLO 60.  The 51 mm valve on the latex tube was fine as is when running the training wheel with disc cover.

For my spare, I would carry a standard 48-60 mm butyl tube (you don't want to use latex as your spare), with a 32 mm extender already attached (with plumbers tape).  If my front flatted, the spare is good to go as the extender is already on.  If the rear flats, I simply need to unscrew the extender which is pretty easy, even with sweaty fingers.  I can carry two spare tubes like this for longer races.

The thing I wanted to avoid was having to carry specific tubes for the front or the rear.  If I carried 80 mm spare tubes, then it would be too long for the disc hole...unless I cut it open.  FLO discs don't have that luxury I believe.  I could carry one of each (one 48-60 mm, and one 80 mm), but what if my rear or front flats twice?  SOL.

ETA:  If using a screw on extender, you always leave the original valve core in the open position, then screw the extender on over it.  Don't worry about air leaking...it won't.

It's easy, but still a PITA.  Mine also require some spacers that I need to keep track of from bike to bike.  Also, as simple as it is, it only takes one time of cross threading to screw up a hub.  I take the stance that even though it's easy, I would not recommended doing it that often.  For 60-100 bucks, you can get one to leave on there.  I would rather do that than risk the ONE TIME I'm careless and over torque or cross thread.

Honestly, I have a race cassette that I just leave on the race wheels.  In most cases, the race course allows for a shorter gear range and smaller gears so I have one just for that.  All my training wheels have bigger gears since I train in hillier conditions and for training, I don't care if I'm one gear less on the small side.

same here.  cassettes aren't that expensive.  I put a cassette on both wheels. Last thing I want to be worried about the night before a race is swapping cassettes.  It already takes me forever to organize all my crap.