Looking at your itinerary I do indeed think that that a 7 day JR-Pass is best suited for your travels. This to cover your travel from the 21st to the 26th.
Here are some recommendation you could consider.
Assuming by Tsukiji you mean a visit to the fish market, be sure to come early, these days only a maximum of 200 Tourists are allowed inside, so be prepared to come early, before 5 a.m. if you can.
Also on the same day when you visit Roppongi and Tokyo Tower, you can walk from one to the other as they are rather close. If you have time after that consider a visit to the ''New Tokyo tower'' better known as he Tokyo Sky Tree, it is an interesting comparison.
On the 20th if you can still meet your friends you could visit Disney Sea, the Disney park in Tokyo is actually 2 parks, Disneyland and Disney sea, both worth a days visit. Otherwise a day trip to Kamakura is a very good option, it is about 900Yen from Tokyo and you can see some marvellous temples and visit the Big Buddha.
I think that for the rest you will have a very nice and trip and I am sure you will see a lot!
Let me know if you have more questions :)
-Daniel