Moving Hosted Excahnge....help!!

Greetings to all.......I have acquired a new client that wants to move her offices exchange account that is hosted, to a new hosted solution.
All local clients run Outlook 2007 and use this hosted solution as their exchange server. She has asked me to take over the IT Support of her office and she wants to move away from the person that does it now.....she is very unhappy with his service.
My thoughts on the process...
1) I need to be sure each client is in cached mode.
2) I need to create a .pst for the entire mailbox for each individual saved locally.
3) These .pst files can be sent to the new hosted solution to create a new mail store.
4) Change the mail server on each local client to point to the new mail server.

Now the new hosted site will change all the MX records so I don't have to worry about that. Is there something I'm missing?

The reason I'm doing it this way is because she doesn't want to notify the other IT company. She's afraid they may do something .....not sure what, but I have to respect her wishes.

Thanks in advance for any insight!!!

Mike