I plan on upgrading to the next gen touch when it's released, but what happens to all the apps I have purchased? Can I transfer them over to the new device and sell my 1st gen, or do I have to repurchase them again?
Anything you've bought once, will always be free. And when you upgrade, just sync from your backup of your old device and you won't lose any apps or saved data when you transfer over. You don't lose anything.
Not everything is free to re-download. Your music you will have to pay for again. Thankfully its super easy to just copy them over.
More importantly... be sure to tie your new device to the same iTunes account as your current ipod. You will then be able to sync all of the same apps to both without repurchasing. No new downloads... they just sync. I currently have two 3G iphones and three iPod Touch 2ndgen tied to a single account. Buy an app once... works on them all.