Absolutely, selecting the right monitors for your setup is crucial, especially when dealing with the nuanced sounds of acoustic guitar and vocals. I agree with looking into the Yamaha HS series or Adam Audio’s AX series as good starting points. Both brands are renowned for their flat and accurate sound reproduction, which is essential for critical listening during production.
Regarding room acoustics, they're incredibly indispensable as even subtle echoes or bass frequency build-ups can distort what you're hearing and lead to mixes that don't translate well on other systems. Since you're in a smaller space, trying to maximize symmetry in your setup can help minimize phase issues and standing waves. Also, ensure there's some absorption material directly behind the monitors and at first reflection points on the walls.
For monitor placement, aiming for them to be at ear level when you are seated is ideal. This usually means placing them on sturdy stands or decoupling pads that can also help reduce unwanted vibrations. The ‘equilateral triangle’ placement where each monitor and your head form equal points is a standard approach that typically works well.
Ultimately, investing time in understanding how your monitors interact with your room will pay off in achieving those clean, accurate recordings you’re aiming for.