So, they run their campaigns with an open targeting and then they trimed the websites to the ones users clicked, and then, selected which ones had better brand value for them. That's simple optimization and they should have always been doing that.
The question arrises when you have to start from scratch. They would also have to start with an open targeting to learn what performs for them.
Simple: I just don't see the point on using these new TLDs, they are confusing, it's not clear how the work and stupidly expensive... Seems just as an snobby thing.
Nice initiative, please consider adopting IAB standard ad sizes like 300x250, 728x90, 468x60, etc so you can access to more remnant inventory.
Right now many ad companies use Greenpeace or Red Cross for serving something when they run out of ads. It shouldn't be hard to get some impressions from them, but the standard ad sizes will be a common requirement.
You can, there are plenty of XML feed providers who will provide you an XML of ads relevant to the keywords you provide, which you collect server side and display to your users.
Are you sure the Garden Hose has free access? I can't find any public access to it in the docs, everything directs me to their "data partners", which charge for this information.