Hey Pocohantas! I will try to answer your questions.
On a cruise share, one person has to take on the responsibity of reserving the boat. (I will refer to this person as the "host" and the others as "guests.") This involves a credit card guarantee. There is a 24 hour cancellation policy. So, if you are the one to "host" the cruise, you could always cancel if you don't get enough people to share with you. Or you could just enjoy having fewer people on the boat and pay a little bit more. IMO, it is appropriate to charge each guest 1/10 of the cruise cost with the "host" absorbing the extra cost if the boat is not filled. That way, each party knows their share and don't get any last minute surprises.
I have read various ways of arranging payment. The actual payment for the cruise is due at the dock at the time of the cruise (the credit card is for guarantee only). Some hosts ask their guests to pay in cash at the dock. Others ask for guests to send in their money via paypal or check ahead of timne to guarantee their spot. I struck a middle ground with my group. I requested that each group send in half of their amount via paypal as a "deposit". Paypal provides a bit of a safety net for folks and allows them to pay by credit card. I am asking each group to bring the remaining balance in cash to the dock that night. Each group is responsible to tip the boat driver at the end of the cruise.
Wishes cruises leave from various docks around Bay Lake/ Seven Seas. I believe it is determined when you book. We originally had a Wishes cruise booked and it was to leave from the Contemporary but others leave from WL, GF, and Poly. Illuminations leave from Yacht and Beach marina. Some hosts choose to share the exact launch info only after payment is received.
Illuminations is viewed from the water just under the International Gateway Bridge! I think that it is this upclose view that makes Illuminations a more popular cruise choice.
Starting in March there will be a new option that may make it easier for folks who want to take these cruises (although it sounds more expensive). From wdwinfo.com:
The Magical Fireworks Voyage, which has been offered exclusively to guests traveling as part of a Grand Gathering group (8 or more), will become available to all, regarless of party size, starting March 1, 2009.
When this change goes into effect, the price will increase to $53.99 per person ages 10 and up, $30.99 per child ages 3-9.
It is expected that this experience wil undergo some changes, including a new name. Stay tuned to the DIS for future updates.
Hope this helps! Have a great trip!
Have you found anyone to join you on the cruise? We have a party of 6 adults that may be interested. I know the cruise is soon but I thought it wouldn't hurt to check. Please e-mail me at with my username atyahoo and let me know. 
