For those who are going to see the magnificent sakura in Tokyo, Ueno park is ready for view. Both my friends went there and they witness the awesome nature.

You are exactly right.  Usually at night i try to swap back to my own sim card to check SMS notification if i received any missed calls.  You get 200MB per day, after 200MB used, the speed throttled down, but unlimited quota.  Basically after exceed 200MB, even to download a whatsapp video willl take a while.  It reset at 12 midnight.  200MB per day is sufficient if you dont watch video.

U mobile sim card.  Look for booth like these in airport.

if the kiosk run out of it, i got mine from the lawson minimart at airport.

Pure data.  That number cannot be called.  The alternative i use is whatsapp call.  It works when i got separated from my other friends.

Q1:
Yes, its not easy to look for currency exchange places in Japan and a lot of it has been converted to machinese. It can also be done in ATM in post office, 7-11 etc.

If its Tokyo, I doubt you'll have problem. Why not withdraw your money in US and change it in Japan?

You may want to check this out for Tokyo.
http://www.therealtravelers.com/japan/toky...ngers-in-tokyo/

Q2:
Credit card - depends. If you're dining in Hotels or upscale restaurants then yes, you can swipe your card. You can also use CC in drugstores (pharmacies), shopping malls etc. Since there's no extra charges incurred, use it for your shopping however cash is also very important because you'll need it for topping up your IC card (SUICA/ PASMO), paying in medium to smaller scale restaurants, buying food/ items in stalls/ convenient stores and many more.

If only 1 day, consider this but it does not include the transport from Shinjuku to Hakone: http://www.hakonenavi.jp/english/freepass/kaizoku-ropeway/