I went to Iceland in March a couple years ago. It's a good
time to go to avoid lots of tourists, but it is on the cool
side. Fortunately, nearly every town has a heated pool and
"hot pots." I didn't take a tour, but I stayed on the ring
road. If you want to go to the inner part of the country,
you'll need a 4WD. I'm not sure what advantages a tour would
give - except make plans for you (I prefer to do my own.)
Lonely Planet and Insight Guides have good books and English
is widely spoken. I also had thought about going to
Greenland. But I was warned that air schedules can be
unreliable and there was a chance of flying there and
getting stuck there - bad if you have a limited time.
Instead I took a little trip to the Faroe Islands for a
weekend. If you have some specific questions, please let me
know - I really enjoyed my trip!
Marguerite in Chicagoland