The oak,
Osaka and Tokyo are a bit of a distance apart, depending on how you will travel there each time will be different.
Tokyo hostels and hotels are cheap with sakura 40-100 night or sleep in a capsule for 20. If your looking for a double for osaka I wouldn't mind.
Plenty to see and do in Japan whether your into cars, anime, electronics, castles etc. 14 days should be fine but you will not be able to see everything.
Speaking Japanese will help but the younger generation is alright if you speak like a simpleton, haha.
Shopping, how much money do you have ?