Why do you need the storage facilities, especially in those two places? The lockers tend to be on the small size, and the larger ones get snatched up quickly, even at stations that are larger than Kamata and Shinjuku-Sanchome.

If you have checked out of your hotel, the hotel will usually agree to hang onto your luggage until you are ready to move on to your next destination. The same is true if you arrive at the hotel before check-in time. Even the cheap business hotels will do this.

If you don't want to carry your luggage while traveling between cities, put your bare necessities into a small bag (if there's anything that's easy to find in Tokyo, it's shops that sell bags of every description) and have your hotel send it to the next hotel by takkyuubin. The cost will be about ¥2000 per bag. This is not at all unusual, and hotels know that they can expect the takkyuubin service to deliver a couple of suitcases every day.