I am inferring the OP is a budget minded traveler from talks of taking Keisei main line (limited express) and lodging in Ueno.

If the b rooms for 1000 yen per night offer is still available, you can consider the Ochanomizu location. It's within walking distance to Akihabara, a direct express train ride away from Tokyo and Shinjuku stations. Getting there is not too bad. Take Keisei main line (not the Narita Access line) to Keisei-Yawata and transfer to the Shinjuku line and alight at Ogawamachi.

Asakusabashi area business hotels are good too. I have stayed at the MyStays Inn property myself. Take Keisei Access or Main line to Oshiage/Aoto/Takasago and cross-platform transfer to Asakusa line to Asakusabashi.

Some things to do:
Visit Tokyo Metro Government Building's free observation deck. It's in front of the Tochomae station on Oedo line, or a hike from Shinjuku station.
Eat at Ramen Jiro. Ask for yasai mashimashi ninniku.
For people watching, I think Harajuku Takesita doori on a Sunday is better, but you won't be there on a Sunday.