How will the room influence the sound of my speakers?

All reflecting surfaces and the size of the room will influence the sound. A mix of absorption and diffusion elements will help to reduce comb filter effects, flutter echoes and general reverb time. Mainly the response below 500Hz will be effected by room modes and comb filters. You will need special acoustic treatment (bass traps, helmholtz resonators) to get this under control, but also experimenting with the positioning within the room can help.