Wirelessly posted (8700g: BlackBerry8700/4.2.1 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/100)
1. To a degree you may be able to do what you want, but I don't believe you'll do exactly what you want. Learn about themes and take a look at the today theme.
2. I'm not familiar with the plans offered by different carriers. T-mobile probably has the lowest cost blackberry data plan. In that case, however, SMS and MMS is not included.
3. I like the blackberry. You need to know that it is different. I recommend you browse the forums and look at the questions from fellow newbies. Look for the "How do I . . ." and the "Why can't I . . ." posts.