Ryusendo Cave and Miyako

Hello!

I plan to go from Tokyo to Ryusendo (using the JR pass for the train to Morioka Station and bus to Ryusendo) and from there go to Miyako (bus to Omoto Station and Sanriku train).

1) Is it possible to do it in one day, if I arrive to do it in one day if I arrive to Mirioka at morning?
2) If I have a JR Pass, where do I get a ticket to the bus to Iwaizumi/Ryusendo?
3) Is it ok to buy the tickets to the bus to Omoto and train to Miyako just before the departure?

お願いいたします!
Simon

1) Is it possible to do it in one day, if I arrive to do it in one day if I arrive to Mirioka at morning?

Transportation is very infrequent in the area. You will have to study the timetables well:

JR Bus Morioka-Ryusendo:
http://www.jrbustohoku.co.jp/route/detail/?RID=9#01

Ryusendo-Omoto Bus:
http://www.town.iwaizumi.iwate.jp/images/stories/bus/H27.3.14omoto.pdf

Trains:
http://www.hyperdia.com/

2) If I have a JR Pass, where do I get a ticket to the bus to Iwaizumi/Ryusendo?

The bus is covered by the Japan Rail Pass, so you just board with the rail pass. But the bus is not covered by the JR East Pass.

3) Is it ok to buy the tickets to the bus to Omoto and train to Miyako just before the departure?

There is no other way.

The bus is paid on board of the bus when you get off as explained here:
http://www.japan-guide.com/e/e2015.html

For the train, you buy the ticket at Omoto Station.

Timetable of bus from Morioka to Ryusendo: http://www.jrbustohoku.co.jp/route/detail/?PID=9&RID=17
Timetable of bus from Ryusendo (龍泉洞) to Omoto station (小本駅): http://www.town.iwaizumi.iwate.jp/images/stories/bus/H27.3.14omoto.pdf

Yes, it's possible to do it in one day, the first Shinkansen leaves Tokyo at 6:32 and arrives in Morioka at 8:45, early enough to take the 9:40 bus.

The Morioka-Iwaizumi bus line is a local line, no reservation is necessary or even possible. Just show your pass to the driver when entering and/or leaving the bus.

Then you can take for example the 14:35 bus to Omoto station, which arrives at 15:03, and from there the 15:13 train to Miyako, which arrives at 15:47. No reservation on those either.