Questions about Ascension

I have been searching around and have found some referances to the answers I'm looking for but just wanted to verify a few things.

1. Ascension unlocks other missions only available to people that have ascended?

2. Do you have to wait to be level 20 to ascend, is there a benefit to ascending early?

3. Can people who have ascended still group with others who haven't ascended, help them with misisons, etc?

4. Is the only way to get the 15 K armor is to ascend?

1. True
2. No
3. Yes
4. No

Thank you for answering the questions for me.