1. In the walkthrough it says that if you talked with Buck in his house you can battle your rival again but I can't. Why?
Complete Stark Mountain first.
2. In sunnysghore city you can get a ribbon if your Pokemon has accumulated all of its 510 Effort Values. What are effort values?
Effort Values are hidden ... things... that Pokémon earn when they defeat one. Look for the effort values guide on the site (somewhere in the Psylab, I think).