1. I think you could expect mostly high water during that period you will be at Taneycomo and also on the White. The flooding this Spring has caused high levels of water on the lakes. If you are not comfortable fishing high water it would be a great idea to hire a guide for the day. I would also suggest you have the guide provide some instruction as to flies, technique and other aspects of the water you will be fishing.
2. The patterns you mentioned are all effective on the area tail waters.
as a side note you might consider a trip over to Roaring River State Park near Cassville for a day of fly fishing. Midges, woolley buggers, and small dry fly patterns should hook you up with a few trout and a good place to hone up on your fly fishing skills.