3 other hints
1. Often underestimated: The Automation of a mix.
Rout each section into a summing bus. Now you can "conduct" your orchestra (sections) by shitfing the sliders dynamically. Record these movements and the DAW will do it for you even if there are a lot of sliders. Maybe you don't need any compressor this way. Plus: Crescendos/Diminuendos can be enhanced with this technique as well.
2. A correct EQing (in combination with depth) can save a lot of transparency.
The rule: The farther away the darker the sound. Mix-beginners often have too shiny percussions, brass and other instruments which should play at the back of an orchestra.
I recommend to listen to a lot of mixes with large orchestras. Observe: How do close and far instruments sound in connection with the high frequencies.
Listen here: the closer the more shiny. Observe how dark the choire sounds for example.
I selected this example because a mix can be compared with a foto/video as well: Close is sharp/shiny and large - far is dark and with poor definition.
Try to see your mix as a picture. Which instruments are close which are far placed - overdo the efforts a bit for reaching your aimes.
3. Composers often overarrange their pieces. Try to compose along the slogan: More is less... specially in connection with music which is mainly played as an audiofile over speakers/phones.
So if you have too much instruments which are using the same frequency range you will have no chance to make out any of it.
Which instruments are covering your strings? Lower their volume (see Automation) or delete it.
And a last point: Mixing is an art. Saying this: "art" means "ability" and therefore you need a lot of experiencies to get this ability.
You are on the way: try, observe, try again, compare, change, be patient... and you will be successful.
Beat