32C works well and is fairly comfortable, 35/38C would be great from a comfort standpoint. The loose areas seem to be more common mid/late spring since they start doing trail repairs then. Having a very wide tire would make those areas not so bad.

No need for knobs, slick tires work just fine and don't pick up rocks as frequently. Get something durable though, I've had the little rocks punch through a tire.

I've had good luck with Schwalbe Marathon HS368's and Vittoria Randonneurs. The Marathons picked up rocks very frequently though.