"Also, I’ve read about the high-speed rail from Figueres to Perpignan – Would that be the rail to take from Barcelona into France? Or are there other better routes?"
There are two ways to go by train from Figueres to Perpignan and beyond :
1. regular train from Barcelona to Figueres, change to high-speed train in Figueres-Vilafant. The train continues to Montpellier and Paris
2. fast train from Barcelona to Perpignan with the Talgo which runs along the coast via Portbou and Cerbere. The train continues to Montpellier which is its final stop. The advantage is that it is more scenic and you don't have to change trains until you get to Montpellier.
See www.tgv-europe.com for timetables including journey from Montpellier to Avignon/Aix/Marseille, etc.
Edited: 11:15 am, February 16, 2012