A FL sizing die and a good seating die are all you NEED, that said I normally decap before tumbling to somewhat clean the primer pockets at the same time as the rest of the brass. However it's not really needed. For that I use a LEE universal decap die but am looking at upgrading that to the Mighty Armory unit as I've been hearing really good things about durability and supposedly works a little better in a Dillon.

I personally like Bushing FL size dies so I can control neck tension. But you may want to learn the craft a bit before going that route. Especially with 308, it's a very non-temperamental cartridge to begin with, typically pretty easy to get really good accuracy out of it and quite frankly, you can blow a lot of money chasing different ideas and learning what does and doesn't work well for you.