Well, one thing I know is that it is not  a very good idea to ever have Kiteboarding and Windsurfing in the same sentence and a VS. between them! 

 I am not going to address the vs. issue at all.
I have kited a few times... But I have also taken a few lessons and would only recommend the lessons first... I am sure somebody will be posting soon about that...
Windsurfing is what I can help you with a little... First off, if you scroll through some of the TOPICS in the forum you will find a ton of postings addressing most of your questions you have. You can rent a beginner board from John Dubock. If you look him up in the membership list you can get his email. Just click on his name from one of his postings to get his profile. Jordanelle is a great place to windsurf, however, it has a thermal window this time of year... Deer Creek right below it is the same. The sail sizes are going to be larger because it's not as strong of wind during this time of year unless a front is coming through.
Other Lakes are good, but if you have a condo on Jordanelle, I'd say, just stay there, rent John Dubock's gear and relax and wait for the wind to come to you. If you want to search for it... You can go up to Sulphur Creek reservoir which is about 45 minutes or so from Jordanelle to the east. There is a post below with directions to that....
Now I am going to Florida in a couple of weeks to stay on St. George Island... Would you happen to know that area? It's in the Pan Handle... I would love to find out if I can rent gear there... 
Have fun and good luck...