Sage advice from Nikam
on the definition of Swell to Mixtures. Of course, that full registration would never include any Celeste rank(s). The drone of the lower pedal stops will carry further than the 8' manual stops ... for our sung liturgy for instance, I retire the 16' pedal stop or use it very sparingly.
Some of us do not have the luxury of manual to pedal couplers. I don't have those on my church II/9 Möller - and there's really no need as the pedal stops are 'borrowed' from either the Swell or Great, with the exception of the 16' Bourdon extension (lowest 12 notes). On larger organs, there are usually enough independent pedal stops that one does not need the manual to pedal coupler much. I reserve using the pedal couplers (when I have them available) for special situations like a pedal solo where an 8' Oboe is not usually one of the pedal stops and is coupled from one of the manuals.
Accompanying a choir is much different than leading hymns. Hymns usually need a firmer foundation of stops to lead the congregation. Unless you have a song leader (and fortunately I don't, thank goodness), the organist always sets the tempo and needs to keep that tempo going. If we 'listen' to the people singing, and accept their tempo, by the time we get to the 4th verse we might as well be singing a funeral dirge.
Proper hymn leading also requires the organist to read the text of the hymn beforehand and then register the organ accordingly. For instance, the two hymns "A Mighty Fortress is Our God" and "Away in a Manger" require drastically different registrations on the organ, even as a leading instrument.
As an accompanist, I must switch gears in how I register an anthem. The choir I accompany at my church has a tendency to sing flat, so I must employ a brighter registration - not louder mind you, just brighter pulling on a 2' flute for instance with the Swell box closed and coupled to the Great 8' Bourdon perhaps. The bass section hears the lower notes nicely and seldom wavers off pitch, nor do the tenors who are the closest section to the pipes in my situation.
As a soloist accompanist, the singer is the 'leader' ... always ... they set the tempo and one has to have a good view of the person singing so that they can 'follow' their breaths and anticipate pauses. Okay, there are exceptions ... some 'soloists' aren't soloists at all and need lots of guidance during rehearsal and if they falter (because of nerves) in front of people, we have to be able to support them as best as we can.
So I have three modes as an organist ... 1) leader, 2) choral accompanist, 3) solo accompanist. Each of the three requires a different technique and style of playing which happens over time and we always have room for improvement. Heck, I've been a church organist since 1961 and still need improvement - I'm always learning ... the day I have no need to learn anything new is the day I die.