CRM/Mobile Upgrade from 4 to 2007

We are using CRM 4 with Mobile application studio based app for our sales force. we have customized lots objects and have Z tables and Z bdocs also custom VBA code. and plan to upgrade to 2007 with .Net mobile client.

My question is ---

1) how would it benifit us mainly from end - user point of view?

2) what should be the steps to upgrade and how big of a deal it will be?

if there is any document available please forward it to me.or if anyone have experience with the similar upgrade please share your experience.

-Thanks

Hetal