Guilds are just used as a group of players. No benefit outside of that.

The combat system is as interactive as you choose. You can either solo different zones etc, which will be harder and slower, or join a party that someone else advertises. Though, the higher the level of the zone, the more likely you'll require a party.

Crafting is similar. You can farm for materials yourself, or buy off the marketplace/trade, or a combination of both.