Welcome to Aximsite!

Congratulations on your purchase!
I personally would roll back. 2003se is more than capable of handling the tasks you want to perform. I tried upgrading my X50v to WM5 and had nothing but troubles with it. I've since rolled back to 2003se.
Some essential applications that I would recommend would be:
Pocket Informant
Pocket Breeze
SPB Pocket Plus
I would also recommend that you buy a screen protector and case.
I have the following:
Case: Rhinoskin
Screen protector: theinvisibleshield.
That should be enough to get you started.