I'm planning a 6-days trip to Tohoku region with a friend for the autumn foliage in mid October. Have browsed through the threads here and it seems like there are many interesting places to visit. So many places and so little time. ;) So would appreciate any suggestions/ advice in our itinerary.

Some of the attractions that we are interested in:

Sendai City
Goshiki-numa lake
Tsuruga Castle
Matsushima Bay
Yamadera
Akiu Otaki /Akiu Onsen
Naruko Gorge / Naruto Onsen

Is this too rush for a 6 days trip? We want to go at a leisure pace, so we don't mind going to lesser places.

Tentatively, we are considering some ideas:
1) using Sendai as our base and exploring the nearby attractions
2) go up north and travel downwards towards Tokyo
3) because we only have budget for 1 onsen stay, which onsen would you suggest? Naruko or Akiu?

Any suggestions or places that you think would fit our schedule and interests better are more than welcome! This is our first trip to Tohoku, so any advice would be greatly appreciated!

oh, we will be using the JR east pass (and maybe the Sendai JR pass, depending on the itinerary.

For more information for autumn foliage, take a look here:
http://www.japan-guide.com/e/e2014.html

Assuming you're starting in Sendai, it takes more than 1.5 hr JR from Sendai to Naruko Onsen with a transfer in Furukawa, about 2 hrs if going further to Nakayamadaira which is slightly closer to Naruko Gorge. There are buses to the gorge from either Naruko Onsen or Nakayamdaira if you don't want to walk 30 min. To enjoy the view of the gorge with the classic postcard view of the bridge and the mt. will take at least 1 hr. hike. Even if you don't mind rushing, the above will take you the whole morning, bearing in mind you have to take into account the waiting time for train transfer and bus connection.

As for the onward journey to Ginzan Onsen, the latest shuttle pick-up time for most ryokans is 15.45. JR journey from Naruko Onsen to Oishida takes 1.5 to 2.5 hrs with a transfer in Shinjo. To be on time, you have to leave Naruko Onsen before 13.00 at the very least. It looks OK but definitely not my idea of enjoying a trip.

Oh, almost forget to mention, the biggest set-back is that you'll miss the beauty of enjoying an onsen stay in the Naruko Onsen area. IMO, both Naruko Onsen and Ginzan Onsen deserve a 1-night stay each.

BTW, have you booked your accommodation yet!? Though you have 4 months, but autumn is a highly popular season. esp. in Ginzan Onsen. It's extremely popular and there are only a dozen or so ryokans there. So you better book ASAP. We went during winter time and although we booked almost 3 month ahead, our first choice was booked out.