With DroidPlanner running on tablet (touch-screen access to all Flight-Modes), it hasn't been a big priority for me, but I finally got around to setting up all my Flight-Modes and Logical Switches on the Taranis (using OpenTX Companion).
They are now on 3+2 switches.
My Flight Modes for AC 3.1.5:
1. Stabilize (SD-down)
2. Loiter (SD-up)
3. Alt-Hold (SD-mid) (SG-up)
4. Drift (SD-mid) (SG-mid)
5. Land (SD-mid) (SG-down)
6. Auto (SC-mid)
... and in Extended Tuning:
CH7 = Simple-Mode & Super-Simple w/ GPS (mode modifiers)
CH8 = RTL
(both of which have own dedicated Taranis switches ... SE & SF)
So, how did I come up with this? Well, my main-mode switch does my 3 favorite Flight Modes. Up (to sky and GPS sats) and Down (to ground and me) are the easiest to find (without looking). If left in the middle (it holds a hover and it's altitude ... I use this a lot). Also, now with the secondary-mode switch, it can be changed to 2 other more rarely used modes. RTL is on it's own switch (easy to find for emergencies), and so are the 2 Simple-Modes. Finally, a separate switch for Auto-Missions.
It helps to write down "the logic" of what you want before starting. This is how I did it (with some help from ScottFlys as I was learning).