I know I'm nowhere NEAR that point of the game, but I gotta ask the question anyway...
Can you rematch Gym Leaders more than once?
Anyhow, the most important things that happened to me since I last posted were:
(1) Got Leafeon!
(2) Got Golem!
(3) Reached the Safari Zone and did Baoba's Owner Aptitude quests.
Right now, I'm grinding in the grass below the Safari Zone, then it's off to the Olivine Gym!