A lot of this is down to taste.
It’s best practice to have the 3rd and 7th in the voicing as these are the essential chord tones. However, this is not a ‘set-in-stone’ rule.
Based on our taste we can choose to include chord extensions and also alterations in our voicings.
The alterations b9, #9, and #5/b13 are particularly useful to add more tension to our dominant voicings. You might like to check out these 2 practice series for more info on rootless voicings and the specific alterations that we can include:
It’s important to familiarise ourselves with the sound of each alteration, and how they change the flavour of the chord. We can then make more informed choices on when to include them in our voicings.
Here’s a few lessons on left hand voicings by myself and our other teachers:
As you will see, there is no definitive way to play these voicings but the above lessons will give you some insights into the different options available to us.
We have the creative freedom to choose the number of notes we include (2, 3, or 4), the extensions we include (unaltered 9ths, 11ths, and 13ths), the alterations (b9/#9/#11/#5), and even the spacing of the notes to create different textures.
I hope this helps Niall - check out those lessons and let me know if you have any further questions.
I do like the idea of a rootless voicings cheat sheet and it would certainly be possible to create some rough guidelines in PDF form so leave that with me.