First off, nice summary about classes. I think it's nice that we finally have something about classes on the forums, even if it's just a small step.
Mana problem solved:
The preist (Healer) is actualy very hard to play. If you don't have bless heal for your whole party, it's insanely hard to heal 2-4 people at a time. Then you have to ALWAYS have alot of mana potions. There's IS one thing however, i don't think is fair. How much damage it has, and its skills. If you use blood beam, it's about 2x as strong as regular attack, and recharges as fast. I have a lvl 34 preist, it can do up to 1.2k damage already, that's not fair.
Level 50 skill for priest = 10% of max HP and MP healed every 10 seconds.
If you have a high amount of max MP then you don't even need mana pots. Also, you can use Saint's Blessing without it draining your MP (Saint's blessing = 30% healing increase at level 5).
Damage problem solved:
Actually, in two ways. ;P
Get a frag weapon. This is completely and entirely obtainable even for non-AP spenders since all items are dropped in game. Frag weapon alone gives massive amount of healing and magic attack.
-If you can't or simply don't want to get frag weapon, then the next best option is to get Savage / Slayer weapon (obtained from General Kahn in Starglade). While this weapon does offer incredible boosts at higher levels, it doesn't match the frag weapon sadly.
-Additionally, AP spenders can get a Crystal Enhanced weapon for 200 crystals. While it's definitely not the best weapon in the game, it's way better then any weapon you'll find for early levels.
Work on your soul. This is the best way to permanently increase any stat you want. For priests that want to solo, increasing your brilliance soul (beginning at level 40) is the best way to get damage fast.
I've made a soul development guide which can be found here
for those that are interested. It also features every soul in details and what stats you can get from each one.
I'm personally a pure Holy priest and I can solo runs just by using what i listed above.
On a side note. Healing is hard to get used to for some people but I fine it pretty easy. You can click on their icon in the party list to quickly select someone individually and for most cases, you really only need to focus on the tank while AoE(mass) healing the party. I've played other games where buffs ONLY last 30 seconds and u have to focus on everyone in party instead of just the tank. This game is simple compared to that.
Anyway, I don't know a lot about any build other than priest but hope this helps.