Hi Mickey,
I'm not in the Osaka or Kyoto district so don't know the hotels very well. Maybe someone else can jump in here with any feedback about that.
I have visited myself though and the distance between Osaka and Kyoto by train is only about 30 minutes so its no problem if you want to spend all 3 days in one place. Which place to stay in I think depends on your preferences.
Osaka is definitely more of a modern city than Kyoto and if you want to go for a drink in the evening and hang out then the Dotonburi area of Osaka is good. Kyoto has more of the local type shops and is quieter I believe - I can't say for sure as we stayed in Osaka and traveled to Kyoto by day to see the temples.
A picture of Dotonburi is here courtesy of
Osaka Blog Luggage on the shinkansen is difficult. For safety reasons (bomb scenarios) the luggage areas at the ends of each carriage are now closed - you cannot use them. Any luggage you have must go with you to your seat and you are not allowed to block the aisles.
If you are coming in to Narita Airport you are able to send your luggage on separately to your hotel leaving you free to get around. I would think that Kansai airport has something similar. This is the link to their
faq page