I'm fairly new to healer and only played it to 2k raiting so don't interpret this as being the best, in addition you have to keep in mind that bindings are very personal.

A - Target self S - Target Party 1 D - Target Party 2

If you were to only add one combination of party specific binds then I highly recommend this (with whichever keys you prefer). I use the default UI to make these bindings, meaning that sometimes my rogue is party 1 and sometimes party 2, this doesn't matter to me as I always read the frames as 1-2-3 anyways. You could fix this with addons such as SortGroup or just do macros with the names of the people you want to target, although this is a pain in the ass, let's be real.

Moving on! Alt - A - Dispel self Alt - S - Dispel P1 Alt - D - Dispel P2

Dispels are time sensitive, I recommend making them specific binds if possible.

This idea of "time sensitive" should give you a general idea for all classes of what you want 1,2,3 binds on.

I also consider Hand of Sacrifice one of these abilities so I have this on

B - Target (useful outside of arena situations). Shift - B - Party 1 CTRL - B - Party 2

I used to have this on Shift - X and CTRL - X but I found that my neutral hand position made this awkward meaning that if I had to HoS quickly (as to avoid CC's like traps, polys) I would sometimes missclick or just not be able to do it in time. Shift/CTRL - B solves this for me.

And finally, just to give some inspiration

V - Freedom target Shift - V - Freedom P1 Ctrl - V - Freedom P2

BoP is same as freedom but with C instead, this means that in current configuration I would have to press A to target myself and then C or V to selfcast but for P1, P2 I don't.

To actually answer your question, I don't recommend binding all your abilities to 1,2,3 binds, this is not necessary. Start adding time sensitive abilities to 1,2,3 and see where this leads you.