I'm looking to configure OrganTEQ for an early music rehearsal in place of a chest organ. Typically, these have four stops that are applied to the entire keyboard, and have a gentle, softer sound. Can anyone recommend a good starting point for this goal?

Well, to start with you don't have much space. So that means your only 8" stop is going to be a stopped pipe of some type, like a bourdon. Most of these will also have a 4' principal of some type, otherwise it's going to be hard for it to carry in a room. After that, it varies. If you want soft, then adding a 4' flute or koppel flute would be nice. There's lots of options for this, as a 4" rank isn't that big. Finally, most of these have at least one higher pitched stop for when you need a bit more power. Popular options are either a 2 foot principal or flute, or a 2 2/3 mutation, voiced either as a flute (more nasard tone), or a quint (more principal tone). If any of these is too loud for you, voice it quieter.