Does the 20% heal/shield power stack with 10% heal/shield power?

Not sure what you're talking about so I'll just take a 50/50 shot and say it does.

stacks with and stacks with and stacks with and stacks with windspeakers blessing (additively).

Multiples of the same item however won't stack.

Crucible and ardent. do they stack?

Yes

You can stack ardent, crucible, windspeakers, redemption. All can stack together. Just no duplicate items.