Keep it simple. I'd opt for ORTF with no spot miking at all on that (accompanying) piano, which is likely at the front. But at least keep any spots on separate tracks, not baked into the mix.
To ensure that no section dominates, place the mics behind and above the conductor, with the choir in a gentle arc, not an extreme U-bend, with the choir rows on risers to allow the mics to see every face. And aim the mics at the rear row singers. Typically the choir edges might subtend an angle of ca. 80 - 90 deg to the mic array. Allow yourself time to tweak things for a pleasing direct/reverb ratio..but if it's too dry you can 'fix it in post' :-).