Yes, you can use the JR Pass on the Yamanote line (Tokyo loop line that goes around Tokyo and serves most of the big stations), the Chuo/Sobu line (Runs accross the Yamanote loop line from East to West) and the Tokyo Monorail. You can also use the JR Pass on other JR Lines that go [...]

You will reserve your seats in Japan. Seats can be reserved at Seat Reservation Machines, ‘Midori no Mado Guchi’ ticket offices, Travel Service Centers and JR-Associated Travel Agencies. You can make seat reservations right up until the train departs. You can read more here on seat reservation

The calculation is based on the day and not time. It doesn’t matter what time you start the pass, it will run out at midnight on the final day. For example, the 7-day pass that starts on January 6 at 1pm will still be valid until January 12 at 11:59pm – not January 13 at [...]

No – and it doesn’t matter which pass you buy. You can only use it for consecutive days after the start date. Even if you choose not to use the pass one day, you will not be able to keep the day for one later in the week. For example, a 7-day Japan Rail Pass [...]

The start date does not have to be on the date that your voucher is exchanged. You decide the date that you want to start it on but this does have to be within 30 days of making the exchange.