So Ive been gone a good long while and when i came back I saw that a Celestial powerset had been added. Seeing as I now have to go back and relearn most of the game anyway I thought i would give this power set a spin. Anyone have have a build/tips for playing this? It would mostly be pve solo but I dont object to grouping once in a while to heal :)

Bron has a tip or two or one hundred and forty seven: Bron's Guide

Force Cascade + Acension = win!

Also, using the support role works great with it.

Q. With the Sentinel role, do the +20% Healing Powers and -20% Damage cancel each other out when doing damage with Celestial attacks, or is it a simple +20% to healing friends and -20% to all damage?

It's +20% to healing and -20% to all damage, each is a separate function of each celestial ability. The powers should list separate healing and damage values on the tooltips.