Three Quick Accommodation & Travel Questions

1. no, yes, yes, and I don't know.
   
   2. What lockers?
   
   3. Doubtful. Perhaps others will know more.

1. Unless it's written in Japanese they won't even know what it is (and they won't try to find out), let alone give you discounts for such a card.

Bath towels - I would try to go without, instead of packing one and potentially carrying around a damp towel for the whole trip. I weaned myself off bath towels, instead making due with the small (2 ft x 1 ft - 60cm x 30 cm) towels provided at inns or for sale for about 100 yen (US $1) at almost any shop. Once the towel is wet, wring it out and wipe off the rest of your body. This size of towel makes it quick to dry and easy to carry if damp. Or wrap it around your neck to wipe off sweat. You can rinse it out in a sink and use it right away as a bath towel. A large bath towel is a luxury you can do without. Not having one will save you a lot of trouble and space. When you stay at a hotel or ryokan you can enjoy the luxury.

Some capsule lockers will have coin lockers, but a locker that will hold a large international flight-size suitcase will be nearly impossible to find. A better bet will be a train station or the hotel/ryokan staff. If you can, pack lighter. It will save your back and shoulders a lot of pain and make all of your transportation connections much smoother.

Senior discounts - very doubtful. I don't know of any discounts for accommodations. Entry fees to some sites and transportation are discounted in some places. You would have to use your passport as ID and use extreme patience in explaining what you want (a discount). It might not be worth the trouble.