Quick thoughts from the mastermind:
I agree with Kyle, try to get your ticket as soon as possible. It’s cheaper and your not as likely to bail out. 
29th of April, around 12 pm: Meeting up at Harajuku station for a jam in Yoyogi koen (park) for everyone who’s in Tokyo and wants to hang and start the fun! Then go for dinner together somewhere in the area.
30th of April, early morning: Take of with rental car, traveling up north for the taikai. Going about half way. Stopping at a nice little town, look around, play even more shamisen (hopefully in the car as well, lol), get drunk (optional).
1st of May, morning: Leaving whatever town we ended up in and get our asses over to the inn in Kanagi, where we will be staying for the rest of the weekend.
From here on practice as crazy on our Jonkaras and Kita no Hibiki.
3-5th of May: Rock the taikais in Hirosaki and Kanagi. Forever changing the ways of how a group tournament piece should be played and make our mark in the taikai history! 
5th of May (evening): Epic party, to celebrate all our awards and to get really drunk on Chu-Hai (or other beverage of interest).
6th of May and on: Hang out some more or separate and travel to wherever we want to go.
My suggestion: Be sure to arrive one or two days before the 29th and leave a day or two after the 6th. You might want to see some of Tokyo too, so a couple of days before or after the Taikai events should give you enough time to do that.
The rental car will be driven by me up to Hirosaki where I’ll leave it. So you’ll have to make it back on your own. There’s bullet trains that wont make you disapointed.
Check out: HyperDia | Timetable and Route Search in Japan.
for times and costs.
Something more to think about:
If you want to do some more traveling I highly recommend getting a JR railpass (which only can be bought outside of Japan). It allows you to travel on most of the JR trains with no extra charge. If you go back and forth Tokyo-Kyoto, you pretty much have had your moneys worth. And you can also get around in the major cities on it.
I’ll be back with more info on the approximate expenses for the road trip soon!