My K-70 has been reverted to "default" and is being used for mostly "Astro" these days, but my "Birding" configuration was developed on my K-70 and continues to be in use on my K-3iii.
For use with my Sigma 150-500mm, I set the camera to TAv mode, 1/1500 @ f/8. The shutter speed is to help freeze subject movement and the reduced aperture helps with a slightly greater depth of field. In reasonable light the auto-ISO was never an issue, given the superlative low-light capabilities of recent Pentax cameras.
When the K-70 was my "full-time birding" camera I had this set on all three User Modes, but with different a/f configurations on each. AFS/spot, AFC/spot and AFC/wide area.
Like this I could effectively switch between a/f options with the camera to my eye, a feature I missed on the KP and am glad to have back again on my K-3iii
Whichever arrangements you end up with, make sure to write them down somewhere, so if you want/need to revert to a default setting for any reason you can easily re-instate your preferences later. Remember, virtually every configurable setting is saved in a User Mode, so any changes you make from default will need to be noted.
Whilst in a User Mode, all adjustments are obviously available to you, so you can fiddle around to your hearts content, the on/off switch will act as an "instant reset", so you don't have to remember what changes you've made to your carefully crafted personal Mode, provided you don't over-write it.
Another "Mode" that I've yet to be fully satisfied with is a Monochrome configuration. Others have posted their preferences and I've tried a lot of them, but am yet to finalize it for myself.
Using the supplied "Digital Camera Utility" to review/edit your pictures can be a great help, as the program uses the same terminology as the camera, so if you find you prefer "+2 whatever" in the software, you can take this setting directly to the camera without trying to convert from one set of numbers to another.
Enjoy … it's a great camera