6 nights in tokyo, is this feasible?

Hey, 2 of my friends and I are headed out to Tokyo on the 2nd to the 9th and I recently put together an itinerary for us. Is this feasible according to the holiday closures and railway times?

Day 1 - Tokyo tower and Roppongi
Day 2 - Odaiba
Day 3 - Tokyo Disneyland
Day 4 - fish market, Akihabara, Ueno Park
Day 5 - Shinjuku, Harajuku, Shibuya
Day 6 - trip out to Oigami onsen

We were also planning on getting a Seishun 18 Kippu. Would that be the cheapest option and would it work with all we have planned? We tried not to plan any trips out to distant regions like Kyoto because we're on a tight budget and we didn't want to waste a couple days by traveling there and back by getting the cheap rail tickets. Thoughts?

Looks fine to me except that I don't think you'll need the Seishun 18 Kippu. Looks like the travelling you will be doing is all short trips around Tokyo which would end up being cheaper if you just paid for regular tickets.

the Tokyo tower is OK as long as you don't go in. It is too expensive considering that the view from the top is not as good as the view from the top of a couple of (higher) buildings in Roppongi and Shinjuku West. Try to have your photo taken with the Tokyo tower behind you and in such a way that Japanese signs aren't obvious. That way people back home will think you also went to Paris!.
you will have time to kill between the (very early)visit to Tsujiki fish market and the opening of the stores in Akihabara around 10 am.
It doesn't take a whole day to see Odaiba so you could
have a look at Asakusa (the temple plus the old fashioned neighbourhood a couple of blocks North of it, then perhaps take a boat ride to Odaiba?

A day trip to Oigami? May I ask why Oigami?

I checked some site that had Oigami onsen as a 5 star onsen. Would you suggest any others?

Since you want to travel mostly within Tokyo, I would suggest that you buy a 1 Day Toei Subway Pass (which allows unlimited travel on 4 Toei Lines - Toei Shinjuku, Toei Asakusa, Toei Mita and Toei Oedo Lines and ALSO unlimited travel on Non-Step Buses on 1 Calendar day). From my experience, this 1 Day Toei Subway Pass is sufficient to cover most attractions within Tokyo (Shinjuku, Roppongi, Tokyo Tower, Asakusa Temple, Akihabara (Iwamotocho), Ueno, Okachimachi, etc). Buy this pass only when you want to travel to various places within Tokyo.

For Odaiba, go to Shimbashi station and buy a 1 day pass on the Yurikamome Line (for 800 Yen) which allows unlimited travel to various attractions in the Odaiba region.

If you are at Akihabara on a Sat, sign up for a free tour available on japanican website. I saw it only after returning from Japan and I was beating my chest about it as I was in Akihabara and was lost in the neon lights! If only I knew there was a Anime centre nearby! Well, maybe, next time!!

If you want to enjoy "onsen," hot springs, it's best to stay over in a "ryokan" traditional Japanese inn - which may not be inexpensive, and you need to book in advance. There are some onsen that you can visit during the day, but from a website I spotted, I could not tell if the one you are thinking of has any day-visit available.

For other suggestions, it depends on what you are interested in - temples? (then Kamakura or Nikko), day visit to an onsen? etc.

I can't really speak much for the other 2 in my group but I think we're trying to keep the actual sightseeing to a minimum. With that in mind, I'm actually just planning it so that the sightseeing of temples and such happen while on the way to doing things or while we're in certain areas where we can do things. I think we'd rather experience things than actually go out of our way and look at things, unless its particularly impressive.

As for the onsen, we definitely want to make a day visit to one. http://www.secret-japan.com/onsen/ has Oigami listed as 5 star, but I am unsure whether it is possible to spend a day out there. Both japan guide and secret japan have it listed as a ryokan though, but we have a 6 night reservation already set at the prince park tower and the thought of not spending a night at a place that's paid for doesn't sit well.

Also, planning Odaiba on Friday was one of the last things I planned for, since I didn't really have anything planned at all. If there's something better to do though, please, don't hesitate to suggest.

Thanks for the Subway pass suggstion. That was the one thing I was extremely confused about. I will definitely take note of that and pass it along. Thank you all for the suggestions and information. I feel a bit more comfortable of our trip now.