1

There is an agency just opposite the municipalidad which should be able to put you in touch with a guide. It's "Turismo Shila" and they have a website. There is also "Turismo Akainij", also with website. You'd be quite lucky to find a tour group in any case, not many people venture to Isla Navarino. I was there in late November and I think there were 5 of us travellers on the island!

I didn't do the Dientes Circuit as it was still far too snowy, and very hazardous. There are plenty of other trails but I hear conditions are very boggy (for instance Lago Windhond) and there's a lot of beaver damage on the island, too. It's a stunning place though. If you make it there a nice, friendly and cheap place to stay (cheap being relative of course, this is Patagonia!!) is Refugio El Padrino in Puerto Williams. Highly recommended.

2

A guide will be very expensive and not really necesary if you have experience and good equipment. The trail is pretty well marked and there are a lot of waypoints avaible. Take a GPS for any case