On every product page under "additional info" you can view the compatibility column. In this column we list software OR file types.

For example, if no software is listed, you will see a file type such as PNG, which means that the product you are viewing is compatible with any software that supports PNG.

Once you already own an asset pack, any future updates will be free. 

Sometimes after a big update we will change the base price of an asset pack, but for existing owners there is no fee.

Yes! You can download more than once, at any time. If you sign up for an account you can also view your download history.