My predictions

William's title ... if he does get a ducal title ... will be announced on the morning of the wedding. 

Kate will have access to the jewels Diana received during her marriage.

Kate will receive a few pieces, perhaps a tiara, in the first years of marriage.  The Queen is rather parsimonious in handing out jewels to the distaff members of her family, and may want to wait several years (to see if this marriage will stick) before dipping into the vaults for Kate. 

The Prince of Wales has inherited,  I believe, the Queen Mother's jewels.  He might present Kate with a few pieces from this collection.  He will also inherit the historical jewels, but the Queen might choose to leave pieces to other members of the family.  Most of the collection will stay intact.

Best Man -- William will not have a best man.  He will have one or two supporters.  Prince Harry is a natural, but I would not be surprised if William also asks his father to be a supporter.  William is said to be close to his first cousin, Peter Phillips, but one wonders how close.  William blew off his cousin's wedding to fly to Kenya to attend the wedding of Batian Craig, the brother of Jecca Craig, who was seen as the girl most likely.    The Craig family, including Jecca and Batian, will be invited to William's wedding.

Kate's family will not have to pay for the wedding although they may pay for a few things, such as the wedding gown.  Nor will the bride be sending out the invitations.   The Lord Chamberlain's office handles weddings and funerals.  I am sure the WEDDING button has already been pushed and the office has started the early prep work.  I do not think Kate's siblings will be in the wedding party as British brides tend to have yards of cute little kids in tow.  Pippa and James might get read the lessons.

The ceremony will be conducted by the Archbishop of Canterbury.  Or the Bishop of London, who is a close friend of the Prince of Wales.

The wedding will be televised around the world.  Prince Edward's wedding was seen on BBC America, as none of the US networks decided to take the international feed.  This will not be the case when Prince William gets married.  I am sure the folks at The Today Show are already arranging for their broadcast spot near the Abbey or Palace.    Please do not ask when the wedding will be seen.  The date has not  been announced.  Please be assured:  YOU WILL NOT MISS IT!

Honeymoon.  No yacht, no cruise.  Africa.

Guest List:  There will be guests from both sides of the family, with perhaps a few European royals sprinkled in for good measure.   Friends of the family, schoolmates, professors from St. Andrews, too. William's surviving godparents.

However, it is far too early to know who will be be invited, and who will be attending! 
Oh, the engagement ring is not cursed.  Charles did not select the ring.  He merely paid for it.  He let his bride-to-be have the honors of picking out the ring.  Garrard's sent a selection, and Diana chose the biggest honker on the tray  ... and Charles whipped out  the credit card!  (More likely, a bill was sent to Charles' office, and it was paid promptly.)

.... and before we have a wedding, we will have a birth ... and a christening of the Queen's first great-grandchild.   Autumn Phillips is in the final weeks of her pregnancy, and is expected to give birth in December.  No, the Queen will not be giving a title to Peter in honor of the birth.   The baby will be Miss or Master throw in a few Christian names Phillips.  The Queen will attend the Christening.  Prince William will be a godfather, and he will be accompanied by his fiancee.