It's not possible to answer your questions without more information. Which version of vBulletin? Will there be any additional features/plugins installed? What is the activity level on your current site? Does you current site use vBulletin?
The answer about bandwidth is also dependent on how you configure Apache. You can significantly reduce bandwidth requirements by installing and configuring mod_deflate to compress CSS/JS/HTML/PHP file output, and by properly configuring cache control headers.
Absolutely, if you've not used an SSD before I highly recommend doing so. Install one in your laptop/desktop at home and you'll immediately see the difference. Cut boot times in half, load programs faster, and it does your taxes. The absolute only reason you'd want to use HDD over SSD is simply cost/space.