Would I need another radiator? If so, what would you recommend? I'm using a 5900x and the 3090 fe in a Lian Li Lancool 2 mesh.Sure, you need only the GPU block and one of those Expension sets.
With straight fittings: https://www.alphacool.com/shop/aios...l-eisbaer-tpv-extension-kit-tube-and-fittings
With 90° fittings: https://www.alphacool.com/shop/aios...baer-tpv-extension-set-900-tubes-and-fittings
And you will need some liquid. Tec Protect 2 or Apex Liquid, like you want. I would also buy a small funnel, makes live easier. Than you can connect everything and fill the loop over the fillport on our Eisbaer Pro.
If the Eisbaer pump wouldn't be enough, what would be?It depends on your requirements. My wife's machine consists of a Threadripper 1950X and a 280TI with light OC. That gives me about 500W of waste heat. I cool that with a 360mm ST30 radiator. The temperatures are not a dream, but good enough. You're looking at about 500-550W of waste heat with the 3090 and that. That would be doable with a 360mm radiator, but it won't be a silent system. Actually, I would recommend you a 360mm for the GPU alone and then another 240mm for the CPU if you want to get good cooling performance with as little noise as possible. However, the Eisbaer pump alone won't be enough for that.