You can drag and movearound the boxes on the right of the 3D views. Place them beneath eachother and you suddenly have a lot more space. Now adjust the 3d view layouts and you're good
You have to open Hammer via the hammer.exe found in Steam/SteamApps/Team Fortress 2/bin/. Launching Hammer via the Source SDK has been broken for years.
You can also automatically make all the viewpoints all the same size by pressing Ctrl A. You may also have to double click some of the boxes at the side if you need to resize them.
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