My studio room is of similar size, only with higher ceiling (although acoustically treated). I have spent literally hours and hours trying to capture violin, viola etc. in the best possible way (including today) and in the end (after many enthusiastic intermediate states) always found that using more than a stereo pair does not improve the overall sound, but rather opposite - it blurres it somehow, spoils the clarity etc. Whether it was a second Schoeps pair or a "room" R88 ...
I gave it up today (hopefully
) and returned to a single stereo pair (with Bricasti reverb it will be changed in a true church anyway
)
I am sure that in a big concert hall or church, additional mics would be useful ...
So it may be true also for violoncello. Maybe you could try a simple stereo pair first. I personally like AB the best (since I like a "spacy violin") ...
It is also true that in an untreated living room, the sound of a living room may be quite obvious, so too much "ambience" and early reflections may not be welcome ...