1 & 2) Yes, that Napa valve stem is correct. Any 412 valve stem will work fine. They're made of rubber, so the exact measurements given in the specs are sometimes a little imprecise.
You can also use a 413 valve stem -- these are much easier to find almost anywhere, even Walmart. The only difference is that they're 1/4" longer. 412 stems make it slightly easier to check tire pressure and look a little nicer.
3) No idea. I static balance. The beads are sort of a pain in the ass that go everywhere, IMHO, but some people like 'em. I hear you can recover them by using a piece of pantyhose over the nozzle of a shop vac and slurping them up.
4) You replace wheel bearings when they need to be replaced. It's impossible to go by mileage. What kills motorcycle wheel bearings is abuse and contamination. Motorcycle wheel bearings are basically standard sealed metric industrial bearings -- they're engineered for very high speeds and loads in machinery. In motorcycles, they're very lightly loaded, but they can be vulnerable to water and dirt.
Stick your finger into the bearing and spin the inner part around. If it feels loose or like it's got sand in it, replace. A little bit notchy is normal -- you should be able to turn it easily with your finger. I recommend keeping a set of wheel bearings in your garage so you're ready to replace them when the time comes. At around 30,000 miles, your odds are good they're OK unless you've been bombing through mud bogs and rivers and blasting the wheel hubs with a pressure washer.
2002 Suzuki DL1000 V-Strom, Dark Metallic Space Blue
1983 Suzuki GS850G, Cosmic Blue
2005 KLR685, Aztec Red - Turd II.2, the ReReTurdening