Entirely dependent on the parts and shop, but here's what we did for our Haas DS30Y.
TL;DR - get at least one, if not two, dual-spindle radial live tools (we are happy with WTO), for much better chuck clearance and doubling your available tools. Try to get at least one similar axial holder - dual-spindle on one side if you do not have a subspindle, or quad-spindle with two on each side if you do. Then add in at least one or two regular radial and axial holders.
We have two regular, single-spindle radial holders and two regular axial holders. Then we have one radial holder with two spindles, where each spindle is offset from Y0 by 1.378", and an axial holder with two spindles on each side - two for the main spindle, two for the sub. Obviously a pretty penny. Pretty much twice/four times what a single-spindle live tool costs! ($5k for the dual radial/$10k for the quad axial) So with everything, we have about $21k in live tools (as the Haas lathes come with one each radial and axial), I wish we had more. At least a second dual radial holder.
Those two multi-spindle tools get way more use than most other tools though and I would highly recommend giving it a look. Costs a crap-ton of money, but lathes are so horribly limited with tool stations. By the time you have OD turning, threading, cutoff, a drill, a boring bar, there's almost half the turret.
There's another huge benefit to the dual radial holder as well, it has much better chuck clearance than plain holders. Using the stock 10" chuck, almost any time we use a regular radial live tool, the tool has to be put in some kind of extension. Making it even less rigid etc.. The dual spindle units extend about 3.5" from the turret face vs. about 1.5", pretty huge. If you're smart and use a collet chuck, that may be a non-issue.
The only issues with these multi-spindle live tools are, A) if you have to move much offset from Y0 for the feature, you're a lot more limited. In our case instead of +/-2", we have about +.620/-3.38 or vise-versa. B) is clearance, as you now have two tools in the same station. It can take some jerry-rigging to get the clearances right.
Thing is, it really can be tricky to have enough tools, even with all this. If you have a part with a drilled and tapped hole in the side, that's two tools. If it has another size hole, there's another drill. If you want to chamfer these holes, that's all four tools (if you have four like we do). Same for axial. Just having two different sizes of tapped holes can wipe out four live tools.