Terms like 5 part drop 2 etc are not orchestral terms really, more big band/jazz (sax arranging in particular) I've found, although I can obviously see their application (I know, I'm a pedant
).
As you will undoubtedly be aware, vertical spacing is intimately linked to the musical effect, timbre and dynamic you are after and only you can answer that Matthew. Once you decide on those three factors, knowledge of individual instrumental techniques and combinations thereof will guide you in the best way to achieve the effect you're after. Best of all though is to write for the combinations at the composing stage, that way your music is immediately informed by the instruments and vice-versa.
So, I'd start there. If you want a jam packed ff chord study scores, if you want a delicate pp colour thinly spaced...study scores....get the picture. There are classic guidelines such as juxtaposition, enclosing and so on but that is only a start to realising the possibilities. Study and listening (with a score) my friend, its the only way. You could develop a learning course for yourself that for example, just concentrates on wind spacing, do the same with brass and then strings. Then, look at how the sections are combined in the scores you've just studied, say brass + wind, then strings and wind, who's doubling who and why - you get the picture. Take note of the musical context, dynamics and where instruments are in the vertical field at a given dynamic. Doubling - is it unison or at the octave or more - why? How many instruments on a particular note, is it an important note musically? Does the harmony of what you are studying have a discordant interval in it? How is that treated?, same/similar colours or different.? Is the chord foreground or background, the answer to that will be crucial to how a chord is treated in terms of spacing and timbre. Are there gaps in the spacing to allow important lines to come through? Is the chord percussive or sustained? Does it have moving parts in it if sustained and how are they spaced? Are those moving parts foreground or background and do they have space around them or not? ......jeez I could create the longest post ever on this. You'll have to use your initiative Matthew - study deeply, inquisitively and consistently (in other words...practice, practise) and over a prolonged period of time because this ain't a few youtube vids and you're good to go scenario if you want to do it well.(Not suggesting that's what you think btw, just a general comment).
Vertical spacing is also inextricably linked with voice leading as chords will in all likely hood move to elsewhere in similar spacing/combinations. For best practice there you need to have a good knowledge of counterpoint and/or a great sense of musical line allied to knowledge of harmony and harmonic resolution.
As
@Saxer implies above, the best scoring will be good for the players because it has at its heart , solid, practical voice-leading and a musical sensibility.
Sorry, I've gone on a bit but the subject is vast and the rules (no, not rules as such, just tried, tested and proven practice) are open to abuse (in a good way) by the imagination, but only after you have understood and internalised them because only then can you make them work for your music.
BTW...Korsakov is a good read with fine examples of clearly delineated and well spaced, judged scoring...he was a master after all.