A lot of the information given is solid so I’ll just add the bits that I can.
Panning isn’t needed… this is true, but the more you add to a piece the more space is occupied. So I’d suggest a stereo widener for things like woodwinds and high percussion. This will push them out to the side more and actually help your reverb sit better on those tracks.
Another tip for panning is related to reverb. As you probablg already know, it’s best to use a few different reverbs in your piece. I tend to have one reverb per section… unless it’s strings, which I have 2 reverbs, OMD for violins and violas and another for cello and DBass. I often pan the reverb for that specific section slightly opposite in relation to where the instruments are mainly seated. So for woodwinds I’d pan the verb slightly to the right, Violins for the right slightly and cellos and basses slightly to the left. This helps widen the stereo field and it creates a more realistic feel. A tip for the verbs is to think in relation to how far forward or back the instruments are seated. A longer verb is better for woodwinds but strings are typically at the front, so the verb would be more of a room sound.
In terms of layering, you could take this many different ways, depending on genre. Though I’ll approach it as if you are writing a more classical piece.
Typically I’d say you need one dry and one wet library… and when I say this I actually mean one dry chamber sized orchestra, and one larger lush sounding Orchestra. This is because typically, a dry chamber orchestra will have more detail but less girth, where the bigger orchestra will have the size but lack some detail. Blending those libraries together will give you that smooth detailed sound you desire.
However, it’s foolish to think you need this approach in every piece you do. Some pieces might just require the chamber orchestra as they sound more intimate, and others might require just the wet orchestra because they often sit better in a mix. It all depends on your needs. as for brass, it’s the same… but you can get away with just having the dry orchestra l library for woodwinds as they are smooth and don’t require that huge sound in most circumstances.
I hope this is of some use.