When do you advise to use this method?

I'm only manager level 2 and training level 24.
The amount of tokens wont be a problem, but when would you advise me to try out this method?
(negos is available from trainer level 4, so i need two more seasons)

Also, i havent tried to train a player up on a Special Ability yet, is it better for me to do that when i get more training levels (and maybe my training facility higher too? it will be L6 in a few days), or is it good to do that whenever i want?