I've found PiP swap to work the fastest when regions are the exact same size.
It is a little slower when the ratio is the same, but the size is different.
I've not experimented with different ratio's but assume this would work too.

As far as follow goes...
You could disable the default movement keys via Keyclone (Do Not Pass List) rather then in Warcraft.
That way, no matter who the active toon is, those set of keys will move that toon but none of the others.
If you do it from within Warcraft, then a PiP swap leaves you with keys to move one slave only, but not the new main or other slaves.

Other follow methods people commonly use...
- Make the active toon the Focus, and have all of the toons Follow Focus. Current toon will not follow themself, but all the others will follow current toon.
- Make the active toon the Party Leader, and have all of the toons /follow [target=party1]. Unfortunately the active toon will try to follow a party member too, but you can break this via arrow keys or the mouse. All the other toons will follow the leader correctly.
- I personally use Jamba to control my following. Within warcraft on the same keybind as your PiP switches place macro's which tell Jamba the new toon has become the master of the group. The Jamba command is /Jamba Setmeasmaster all. You can follow within Jamba either on a keypress or have it strobe the follow key every (configurable) few seconds.