Upgrading from 1.5 -> 2.0 do you just upload to your same folder and replace 1.5 files? Same thing with XFMG? If so do you use a new install download of XF2 or upgrade?
yeap.. but have some free time so want to upgrade a second copy of my site to XF2 for testing purposes in the event I decide to upgrade my live site in the future.
Upgrade. As part of the XF upgrade all of your add-ons will be disabled. Upload the XF add-ons (Gallery, Resources) like you would any other update, go back into your ACP, and then you'll be able to upgrade those.
If you're going to play with an existing site you may want to first clean house & get rid of any add-ons that you know you won't be upgrading.