Luggage on bullet train Tokyo to Osaka

We are a party of 4 flying into Tokyo for a few days before going to Osaka to board a cruise ship for a 16 day cruise. We are probably going to take the bullet train from Tokyo to Osaka, but we have 4 fairly large suitcases that we need to take with us. We plan to reserve Green Car seats on the train, but are concerned about luggage storage on the train. We have run into a slight problem, in that having our luggage sent from our hotel in Tokyo to the Port of Osaka rather than to another hotel, seems to confuse the luggage transfer company and we are concerned about the size limitation from them (having to fit into a plastic bag). Does anyone know of a service that will doing "hand holding" to get us on the train, and help get our luggage on the train?

Have you tried the takyubin service? I used it to send my luggage from my hotel in Nagasaki to my hotel in Osaka, and it was very easy and cheap. Just ask your hotel receptionist to help (the form is in Japanese, but can be filled out in English), and make sure you have the address and phone number of the hotel you want to send it to. It will arrive the next day, usually.
If you definitely can't send it, don't worry about luggage on the trains; there is always space behind the last row of seats in each carriage that can hold at least two large suitcases on each side (more if you stack them correctly). Your train will start at Tokyo station so as long as you get on first, there will be space. Getting the luggage through the station and onto the train is okay as there are lifts. I did this multiple times throughout my month in Japan; as long as you can lift the suitcase for a few seconds to get it on the train, you'll be fine!

Thanks so much for your reply.We are going to give the train, with luggage, a try.

You can place your bags by the seats where your legs are supposed to go. There is much space on shinkansens and green seats.

There are overhead luggage areas too.

There are luggage areas between carriages; some shinkansens have locks in these areas.

If you can get seats at the front carriage there would usually be more leg room so you could put your luggage there.

Since when is it forbidden to bring a suitcase onto trains? I read about people worrying about it oftenly here. Tourists and travellers means luggage. Why would it be different in Japan?

Unless each of you carry multiple 28" suitcases, I wouldn't worry about it.

Rather than one very large suitcase, you might find it easier (for carrying, and for luggage storage on trains) to carry a medium backpack and a medium suitcase.

It depends where people are from; British trains have very little luggage space and are much more crowded than the trains in Japan. Four people with suitcases is a major hassle here, so we fear the same in Japan if we've never been there before!

You can place your bags by the seats where your legs are supposed to go. There is much space on shinkansens and green seats.

The space between the seats is large enough for a carry on, however it is not a comfortable way to travel, and if your suitcase fits there it will also likely fit in the overhead shelf.

Personally I prefer to sit in the last row of the train when travelling with larger suitcases, so that I can put them directly behind my seat and keep an eye on them if necessary.

There are luggage areas between carriages; some shinkansens have locks in these areas.

You're probably thinking of the various airport ltd express trains. The shinkansen generally don't have luggage space between cars, unless you're counting the space behind the last row of seats.