Question about Corsair Obsidian 1000D

You can do it however you want. Of course, it's more designed for water cooling/two systems in one, but you can also just install fans instead of radiators or take an AIO, that's up to you. But I would say that there are other cases that probably make more sense or have a better price-performance ratio if you want to use an AIO or just fans. Unless you want a big case with a lot of fans.