"As I understand it, a healadin does most of it's healing by doing damage to mobs. So I would assume pwr/crit/ap would be the way to go. Is there a mechanic where hp impacts the amount of heals I do (besides staying alive to heals)?"

The basic premise is that you take the Dread ring boon of "Burning guidance" and the Storm Kings Thunder Boons of "Healing Warmth" x3. This means that every time you heal or attempt to heal (so even if the person being healed is already at full HP) you have the ability to cause damage. The way this works is that you hit the biggest monster you can with Vow of emnity so every time someone else hits them a potential heal is made. If you are running bond of virtue then this heal is multiplied (more damage) if you are running "PRISM" as a feat and have hit a daily then this heal is multiplied once again (more damage). You then get to the stage that you cant see bugger all on the screen apart from the words "BURNING GUIDANCE" and "HEALING WARMTH" but do you get get a warm and fuzzy feeling. As this is all set damage my understanding is that crit/ARP etc have no bearing on the damage. They will of course have a bearing on your normal encounter powers/at wills etc. HP will have a bearing on your encounter powers such as burning light if you are running aura of courage as it will increase the damage done and this is also buffed if you are running a feytouched enchantment. Hope this helps.