few questions about traveling to Japan

I've read everything i could, but few things I really need to be sure about.

JR pass - can I exchange the voucher and get the actual JRpass to be valid from next day? I will arrive late afternoon and don't want to waste a day.

Reserved seats on shinkansen - If a particular shinkansen doesn't require reservations can i just show up on the platform, board the train and find free seat? I (plan to) have a JR pass.

Shimanami Kaido - I want to take the route in mid November. How 'smart' is this idea weather conditions wise?

Narita express - I plan to buy narita express round ticket (without JRpass). I understand that Nex require reservation. Do i need to make reservation for return trip (Tokyo-Narita) at the time of buying?

Thank you kindly,
T.

JR Pass: Yes, you can pick any start date you want.

Reserved seats: As long as there are unreserved carriages, yes, you can just show up and get on. You can only sit in the reserved carriages if you make a reservation. There are certain shinkansen that always require reservations, so make sure you check beforehand.

I can't answer your other questions - try looking around on this website.

You do not need to make the return reservation for the N'Ex 14-day ticket at time of buying. You can do that at any stage before you use the return leg (which doesn't have to be from the same station).

Also, about jumping on any unreserved shinkansen car, that works for many trains, but don't make the mistake of getting on a Nozomi train for an unreserved seat. The JR pass doesn't cover that.

thanks for your help, just returned from japan.