The Repeater Region is how I primarily heal.
I do have a couple of assist based heals too, for those not in my group.

Assist Heal
#show Rejuvenation
<Insert Assist, or with IS Boxer put on an FTL Assist Key>
/Cast [Help][Help,@TargetTarget][Help@TargetTargetTarget] Rejuvenation



The Repeater Regions is set up like this:



Part A (Grid Addon and Clique Addon)

Grid + GridCustomLayouts.
My custom layout is:

Toon1,Toon2,Etc,Toon39;NAME
1,2,3,4,5;5/5;NAME;NR

I have thirty nine names listed on line one.
The format is name comma name comma name, with no spaces.
It ends in semi-colon and NAME in caps, still no spaces.

Line two is as listed.

This gets me any combination of my toons, listed alphabetically in column one.
Up to five names listed, as the 5/5 forces a five by five grid.

In a raid/battleround, the remainder of the raid is listed in columns two through five.
They too are alphabetical, without any name repeating.

I like to position the frame with Mouse Repeater, so I know its in the exact same position on every screen.

In a 15-man, it ends up looking something like this:

MyToonA... Raid A... Raid F
MyToonB... Raid B... Raid G
MyToonC... Raid C... Raid H
MyToonD... Raid D... Raid I
MyToonE... Raid E... Raid J

In a 10-man, the right most column is gone; in a 25-man, there would be two more columns to the right.

For Clique...
I usually use: Alt, Ctrl and Shift, with Left and Right clicks.
So six keybinds for most of my healing.
Alt Left, Alt Right, Ctrl Left, Ctrl Right, Shift Left, Shift Right.

I try to be consisent, with Alt Left being a HOT, Alt Right being a medium heal, etc.



The IS Boxer portion...

Create an Action Target Group, and put the healers for the team into it.

Press your Repeater Region/Clickbar hotkey.
Go to the Repeater Region tab.
Check the KVM box.
Select from the drop down box, the name of the ATG that will heal this team.

Click create Region.
Drag it so it covers the entire Grid frame.
The red portion (inside) is what counts, not the border.

Click Sync, so it is the same for all the slave windows as the master window we've just sized.
Then Save as Auto, which means it will auto load for this team.

You could resize the Repeater Region to only cover the first column, if you don't want to heal the raid at all.
Or resize it to be your column when solo (5-boxing), but larger when in a raid with more Grid Frames.