Download the .zip file and extract it to a new folder. Do not copy old stuff over from the old installation and everything is fine.
If things are not from the buddystore and streamed automatically, yes you have to and it makes sense. Check the threads if the stuff you're downloading works with latest HB release and wow legion. A lot of things offered are not ready atm. and can cause issues. It depends on the author if he is providing a fix in the free section. For paid store products you can use the 3rd Party support thread of the product to report the issue. You can find it in the store product description.