Discount ticket store

Hello,
i have some questions regarding the discount ticket stores :
1. Im planning to book a shinkansen ticket, is it possible to book an reserved/unreserved seat for specific train (hikari,nozomi,etc), time, and dates?
2. In general, do they only sell the ticket embarking from the nearest station? eg. disc tix store around tokyo sta. only sell the ticket embarking from tokyo sta.
3. Do i need to change the ticket with the official ticket from a JR counter?

Thanks

Shinkansen tickets at discount stores are available both reserved and non-reserved single tickets.
If you buy a non-reserved ticket, just buy and go, sit on a non-reserved seat.
If you buy a reserved ticket, you will need to go to "Midori-no-madoguchi" or reserved ticket machine and then reserve your seat before you get on board.

This discount ticket is unable to use between April 27 - May 6, August 11 - August 20, and December 28 - January 6, due to high peak season.

The tickets are available at any discount stores depending on the demand. Normally, shinkansen depart/arrive in Tokyo sta sell around Tokyo sta, and/or Shinjuku sta, not many people will buy a ticket between Himeji - Hakata in Tokyo due to low demand.

The ticket is set validity date. You can not use after it expired, so be careful when you will buy the ticket.

Those tickets are available between high demand destinations ONLY(eg, Tokyo- Shin Osaka), not available between Tokyo - Shin Aomori due to low demand.
If you want to buy a discount ticket on the destination of low demand, you will need to buy a shareholder's benefit ticket(Kabunushi-yutai-ken) first, take the benefit ticket to "Midori-no-madoguchi" and then you can buy a bit cheaper ticket(20% discounted) include low demand destination. But I don't know how much you can actually can save when you buy a "Kabunushi- yutai-ken" and get a 20% discount. You can buy two single tickets once.

it is not refundable and not exchangeable, because it is not issued directly to you from JR company.
also, you can't claim to JR company, if you fail to use it.
if you don't understand the rule fully, I advise you not to use it.