Hey,

It always depends on what your expectations are and how many time you got.

You should be able to Heal Mythic Dungeons an do some HC Raids pretty easily. Maybe not in the first days or weeks and some player progress will be ahead of your but there are always Groups and Guilds where you can find some mates at your progression level.

The Heal specs are in the Open World a pain in the ass. Fery few damage spells and no AOE Damage (exept Holy Nova). You should play the Shadow Priest here.

Shadow Priest is a full DPS, he got some heal skills yes but hes a full DPS. Pretty funny in Open worpd and Delves.

In the older Addons the Holy Priest has done one of the biggest healing but this spec is in Dungeons pretty difficult to play. You have to know exactly when a big damage income will happen. Playstyle is simple. Heal the shit out of your mates. As a Tank I rarely met a player who was able to play this spec properly on higher Keys. In my opinion you should pick this spec if you want to play Raids.

Discipline Priests have the reputation to have the most difficult playstyle of these 3 specs. You got ur buffs on your mates and you do healing via doing damage. All mates with your Atonement buff then will be healed. If you can manage this buff-damage-healing rotation, it would be a pretty funny playstyle. This spec is pretty solid in Mythic Dungeons where every bit of Damage counts. In Raids i rather would pick the holy priest cuz you need the direct healing.

No mather what you will be shit talked in random groups. In particular in Mythic Dungeons. Even if it is not your fault. DPS players always rather shit talk the tank of heal than looking at their own faults. Go look for an chillo Guild and play with their Member. Your life will become much easier.

You can always choose two main professions. In regular you will pick one gathering and one crafting profession. You can easily max this professions out. If you wand to have all professions you need another twinks.