Welcome to XF2 Addons. You can buy my Premium membership for $35 per year, and this gives you access to download any or ALL of the 250+ add-ons that I have developed for Xenforo 2.x. In addition, Premium members will get technical support. Once the Premium membership has expired you can continue to use the installed addons on your forum as long as you like.
Correct, you could without any issue. The other alternative is to uninstall after you upgrade to XF2. Of course some add-ons have a upgrade path so if you install those XF2 add-ons and it matches a XF1, you can simply upgrade that add-on.