Possible situation will be the chance of all your traveling group not able to sit together. Green car is reserved seat with seat assignment at the time of ticket is issued. Using JR pass means you will not able to reserve the JR ticket till you arrive at Japan, which is likely starting date of your trip. I think getting 10 seats together may become little difficult.
For purchasing regular JR tickets, tickets are sold from one month before the date. However, for group travel of 8 or more get 10% or more discount (depends on number of people in a group) and accepts reservation (actual ticket issue is from one months before the travel) from 9 months in advance, such will assure that group will get seats together.
Above is not applicable if traveling using JR pass. Shinkansen (bullet train) Hikari consists from 16 cars and out of 3 cars are Green Car. I think it is possible that your group will be spread apart, even spread among different train cars.
Yes, when passing through Green Car it is that obvious that Green Car is quieter than regular car. Green Car is not allowed on business travel for non-managers at most places of work in Japan, and there is no such thing as frequent rider upgrade, so especially on Green Car between Tokyo and Osaka tend to be heavier with manager and celebrity type.
Will add one more thing. Green Car seating is 2-2 across, and seats can be turned around to face back. This will allow to make block of four seats facing each other if you able to get two consecutive rows of seats together. However, Green Car seats recline deeper than regular car seats. When somebody turn around seat to face back to make four seats facing each other, then the seat facing the back of turned around seats will not able to fully recline, some may consider that little inconsiderate. I am not sure how many Japanese passengers will voice that to other passengers especially if other passengers are foreigners do not speak Japanese.
