"Steering with the sails" really isn't that hard to master - to head up, sheet in the main and ease the jib. To bear away, ease the main and sheet in the jib. The skill is in feeling
when you need to do it and resist the temptation to steer out of a situation with the rudder that will just stall it.
Here's a photo of Enrique Figueroa (many time North American champion) rounding a leeward mark and heading back upwind:
The technique here is flawless - the rudder's up, Tito (his crew) is already getting on the wire, Quique's hooked and ready to go out - and they haven't even passed the mark yet!
But notice the sails - the jib is almost flapping it's so far out while the main is almost completely sheeted in. Oversheet the main, head up.
As far as having the crew work the main or traveller, it really depends on the skill of the crew and how much they can coordinate with the driver. Once you're both out on the wire, the crew really only holds on to the jib sheet to help keep themselves attached to the boat. They can sheet in, but it's really hard for them to uncleat the jib from the wire to sheet out.
So, most top teams have the crew work the main traveller in puffs. Depends on the strength of the crew, too - on a 16, most crews are women or youths that may not have the upper body strength to manage either the main or the traveller. I'll usually coordinate the crew's traveller moves with the mainsheet - giving the crew an assist when pulling up and controlling the dump.