1. Very top players like Federer/Nadal.... First class on commercial airlines? Or private jets? I'm a little doubtful about private jets because after all they don't earn as much as let's say Brad Pitt or Jon Bon Jovi.
You are so far off the mark.
According to Forbes, last year Roger Federer made US$47 millions (ranked fourth among sports stars after Tiger Woods, Kobe Bryant, and Le Bron James), while Brad Pitt made "only" US$ 20 millions and Bon Jovi (as the whole group, plus agents etc) made US$ 125 millions, and that means Jon Bon Jovi is most likely to have made well under US$47 millions that Federer made last year.
So of course Federer travels with private jet, keep in mind also that he travels with his entourage (wife, children, trainers, masseur, parents, etc), which makes more sense and is actually cheaper in the long run if he buys a private jet rather than flying first class or renting, except if he gets it for free, and as mentioned above, he is sponsored by Net Jets.
Even Maria Sharapova made US$ 24 millions, mostly from product endorsements (Nike,Cole Haan, etc) and Nadal made US$ 31 millions.
Tiger Woods have made US$ 1 Billion in his career, and you can bet all your money most of it is not from winning prizes.
These days the most elite and marketable sports stars are making most of their money from products endorsements.