That's actually pretty similar to how I would bus things when I was doing only TV production music. I'd use a few more groups, but the same idea, and pretty simialr... Any percussion beds would also include pulses, (even braams or bass synths like 808s, etc), and SFX would also be part of the percussion bed. In addition to the main version I'd send a 'harmonic' bed, percussion bed, a version with no lead/melody, (plus cut downs, stingers, etc).
I've been focused only on trailers the last 3-4 years (mainly because it's a completely different mindset, also customization's always a possibility)... I plan on doing more general production music again when the imposter syndrome becomes more manageable
[True story!]). Now I typically have to send stems for everything, (minimum 12, maximum of 24). The stems also have to be an identical sum of the mix, meaning no bus processing, (although I cheat a little and use a little EQ and some Inflator), so I have discrete busses for everything, and all processing happens on the busses...
There are my typical stem busses:
Hits & sub booms (May be bounced together or separate, depends on the cue)...
Drums/large percussion
High percussion (field recording percussion, 'tick tocks', sticks, etc).
Short strings
Long strings
Brass
Choir/vox
Top line/melody (if any... Trailers these days tend not to feature one)
Pads/atmospheres
'Signature' synths (if used)
Any other 'signature'/distinct sounds that an editor might want to feature, or mute.
Bass pulses
Mid/high pulses
Braams (or similar, i.e. 'reeses', distorted 808s, etc)
Lead synth (if used)
Short plucky synths (i.e. 'pings', 'sirens/alarms')
SFX
It depends on the project in terms of how many stems I send. If something is primarily orchestral or organic I may send 12 to 15 stems, if something's hybrid, and has a lot of sound design I may send between 15 and 20. (I believe the most I've sent for a single cue is 21).
As far as mixing and writing in the same session, that's a luxury I wish I had! The mix has to happen as part of the production for a few reasons...
A). Revisions are inevitable. Most cues have 3 or more rounds of revisions before being accepted, (3's the minimum I've received, and it's rare. More like 4 or 5).
When I get to those last one or two notes I'm typically fighting a lot of latency, (thankfully Logic has low latency mode).
B). 'Production value' is (more or less) expected to be part of your v1. Basically, if you wait to mix everything at the end you'll just get notes about the mix as part of every revision, so it's unavoidable. Fidelity can't be an afterthought with libraries who target trailers... And the fidelity really does have to be the best that you know how to deliver.
I do export stems, then bounce final mixes from there, but that's because cut downs are easier with stems, and more importantly, you never know what they'll come back with in terms of feedback until they sign off on it... So exporting stems before they say you're done would be redundant. The last note may say 'do these 2 or 3 things and we're all set', but I don't export stems until they say it's time...
Alt mixes are optional if the cue has no voice. Alts are required for cues with choir, or any other vocal. So a typical orchestral or hybrid cue with choir has two mixes as part of the deliverables, the full mix and a 'no choir' alt mix (as well as cut downs). If a cue does wind up having a distinct top line or melody I'll also bounce out an alt version with it muted and let the publisher decide if they want to include it as an alt mix, (which has worked in my favor a few times... An
Aquaman trailer released a couple of weeks ago where they muted a brass/string top line I originally had in the cue, so it's not just reality TV editors that don't like melodies
)
And although it may seem redundant having alt mixes when you include all of the stems, there is some degree of logic to that... As you said, it's all about making life as easy as possible for the editor. Alt mixes can be useful for targeting trailer houses that may be cutting a bunch of TV commercials for a specific campaign. Sometimes they'll use a cut down as is, or chop up an alt mix to fit a shorter cut...
I'll probably continue to work this way regardless of whenever I get back to writing some more general production music... I'd adapt and solo what I want as individual stems if needed, with trailers though, you have to be literal in how you group your instrument stems... Basically, my busses reflect everything I need to deliver as a stem because doing it any other way is problematic.
Although currently I have to deliver parts with no bus processing, for libraries where stems aren't required, and want me to master things myself then I'd do some moderate processing on the mix buss. A little saturation or tape, some mix bus compression or multiband compression, a little EQ, and some limiting. (Good old Inflator never hurts either).
And absolutely, metering is essential. With the publishers I'm currently working with everything's sent off for mastering, so meters really are critical.