Combining HRTF with echo
Choosing points in the horizontal plane with proper spacing seems like the right approach. Aneochic HRTFs are probably the easiest but typically lead to "inside the head" localization. Depending on your application this may or may not be a good thing. If you want externalization it's best to use binaural room impulse responses measured in a space that's similar to where the actual playback happens (there are psychological reasons for that). However these binuaral room impulse responses are a lot more complicated and require significantly more computational effort.

You cannot binauralize a measured monaural impulse response after the fact. A real binaural room impulse response consists of the direct sound plus many reflections that all come from different directions. So each part of the room impulse response contains many different anechoic HRTFs. There are however computer programs that allow you to put in a geometry, acoustic properties and then they will calculate a binaural room impulse response.