Before you do anything, I would suggest that you read the BlackBerry 101 lectures. If you have any issues afterwards, you will be able to find help on the forums.
if you mean apps-wise i think some apps that are good to have are facebook, crunch sms (better then the native sms in my opinion), and anything else that really catches your eye and improves your productivity. also, a nice theme on your curve would be nice
First thing I did when I had a curve was get a new theme, I dont like the default for the 83xx series. I got the bold inspired theme so I felt up to speed lol.
For apps I would get facebook or myspace if you have those, an internet radio app like Pandora or Slacker. The crackberry app so you have instant access to this site, and an app to find places your looking for like point or where. Dont forget google maps!
I just upgraded two of my (VZW) 8330's to OS 5.0 hybrid from Nathanix and I am very happy. The OS seems more responsive, and the new OS fixes a number of the small annoyances with 4.5.
One of the two was upgraded before the phone was activated (an eBay phone) and the other was already activated. It made little difference in the setup.
Just make sure you do all the steps as described in Nathanix' page and you should be safe.
I like to do that from a laptop rather than the desktop because if you lose power while flashing the device, you may end up with a brick (not sure, but I don't like the idea). With a laptop, the battery will prevent from interrupting the operation until finished.
I wanted to say also that the VZW employee was unfazed when I brought her the 8330 with OS 5.0 to be activated. Either she did not know the 8330 was not supposed to have 5.0, or she did not care. She made no mention of it and activated the phone normally.
