You can randomize in one trigger, but it's easier to do it in 6 triggers
It seems like a good example for explaining what's happening, but I think that's a lot of unnecessary triggers, especially if you want to modify the system later. It is definitely easier in many circumstances (like when you are directly adding a random number of ore/gas/units/score/death counts), but for something that can't be accumulated over a number of triggers (like a random location), it would be less efficient.
Still a good trick to be aware of, regardless

Create 1 psi emitter at location 4 for player 12
Just a note, that wouldn't work. You can't create units for Player 12.
As for the question about not being sure how switches work, they are exactly what they sound like. It's like a light switch, it's either off or on (Cleared or Set). All switches start as Cleared. When you set or clear a switch, it changes for everyone (switches are global, not player specific like death counts). They serve no purpose whatsoever except for you to be able to check them in trigger conditions.
When you go into the "Set Switch" action, you will see there are a few options: Clear (flips the switch off), Set (flips the switch on), Toggle (flips the switch to the opposite of whatever it is already), and Randomize (flips the switch to a random choice).
If you randomize one switch, there are 2 possible outcomes (Clear; Set). If you randomize two switches, there are 4 possible outcomes (Clear Clear; Clear Set; Set Clear; Set Set). Similarly, if you randomize three switches, you get 8 possible outcomes.
Therefore, in the example I gave earlier, you can randomize three switches (Switch 1, Switch 2, Switch 3), and also "Set Switch 4" to activate the triggers after it. Then in the conditions of the 8 triggers which follow it, you'd have something like:
Conditions:
Switch 4 is Set.
Switch 1 is Clear.
Switch 2 is Clear.
Switch 3 is Clear.
All Players commands exactly 0 Psi Emitter.
Actions:
Create 1 Psi Emitter at RandomLocation1 for Player 5.
Clear Switch 4.
Preserve trigger.
Conditions:
Switch 4 is Set.
Switch 1 is Clear.
Switch 2 is Clear.
Switch 3 is Set.
All Players commands exactly 0 Psi Emitter.
Actions:
Create 1 Psi Emitter at RandomLocation2 for Player 5.
Clear Switch 4.
Preserve trigger.
Conditions:
Switch 4 is Set.
Switch 1 is Clear.
Switch 2 is Set.
Switch 3 is Clear.
All Players commands exactly 0 Psi Emitter.
Actions:
Create 1 Psi Emitter at RandomLocation3 for Player 5.
Clear Switch 4.
Preserve trigger.
Conditions:
Switch 4 is Set.
Switch 1 is Clear.
Switch 2 is Set.
Switch 3 is Set.
All Players commands exactly 0 Psi Emitter.
Actions:
Create 1 Psi Emitter at RandomLocation4 for Player 5.
Clear Switch 4.
Preserve trigger.
Conditions:
Switch 4 is Set.
Switch 1 is Set.
Switch 2 is Clear.
Switch 3 is Clear.
All Players commands exactly 0 Psi Emitter.
Actions:
Create 1 Psi Emitter at RandomLocation5 for Player 5.
Clear Switch 4.
Preserve trigger.
Hopefully you notice the pattern and could do the last 3 triggers in that series.
As mentioned earlier, after those triggers, you'd want this:
Conditions:
Always.
Actions:
Clear Switch 4.
Preserve trigger.
This is for the situation where there is still a Psi Emitter on the map somewhere, since none of the previous triggers will have been able to clear the switch.
Also, you should add hyper triggers to your map. They are a set of 4 triggers which make all your triggers run 16x faster, so they become extremely responsive. The only requirement is they must be owned by a player who will be in the game (preferably a computer player).
These four triggers are all identical copies of one another, and all they consist of is:
Conditions:
Always.
Actions:
Preserve trigger.
Wait 0 milliseconds.
Wait 0 milliseconds.
Wait 0 milliseconds.
...
... (Copy the Wait 0 action as many times as you can, until you've filled in the whole trigger. The maximum is 64 actions, use them all.)
...
Wait 0 milliseconds.
Wait 0 milliseconds.
Wait 0 milliseconds.
That's one hyper trigger. Give it to a computer player, and copy it 3 times (for a total of 4 hyper triggers). You should notice an overwhelming improvement in how quickly your triggers are executed.