Healer + Thane is a solid PvE Duo and for sure playable in RvR. Shaman + Thane might be more efficient.
The lack of speed might hinder you in RvR tho.
Skald + Shaman would be one of the best Mid-RvR Duos.
I would personally recommend to level a farming/PvE-Duo first.
Such as: Healer/Shaman + SM/Thane.
They still are fun in zerg RvR.
In case that you really want to run Duo in RvR, go for another Duo.
You will most likely either go stealther Duo or anything together with a Skald (Shaman, Healer, anything else).
Speed 5 (6 with endu reg) is king if you run visible solo/duo.
Regarding your question how to spec a Healer.
There are several viable options, from tri-spec (if you mostly run Duo) over to Pac/Aug or Mend/Aug.
Highest Aug spec I have usually seen so far is 40, in rare cases 44 if you run in a caster RvR group (Midgard, lol). So yeah, not more than 40.
If you want to go for Pac/Mend or Aug/Mend as a focus is your choice, luckily you have unlimited respecs until lvl 50.
Just play around here:
https://playphoenix.online/charplan/?class=Healer&level=50&realmRank=30&view=skills
And ask your theoretical spec.
Healer-race: Stat-wise Frostalf would be recommended. Dwarf usually gets ignored and seen as a melee for the first seconds and eye-patch dwarves are sex as hell.
RvR-group composition usually consists of one Pac/Mend and one Aug/Mend Healer.
Take care as a Pac-Healer (both PvE and RvR), your job is essential and one mistake usually means a wiped group or a lost fight.
Feel free to ask in case that you have further questions.
Have fun.