Need Tips: New to POE, New to Ranger.

Hello. My Elemental Ranger just turned 37. I'm currently using the following skill gems,

Lightning Arrow + Faster Projectiles

Burning Arrow + Weapon Elemental Damage

Split Arrow + Pierce

Poison Arrow + Added Cold Damage

Questions

1) I also just acquired a CHAIN Gem and I'm wondering which will be the best skill to link it with.

2) I also have Wrath and Clarity. Should I be using both?

3) Which are the gems I should / should not level, and what is the best level to stop at?

4) I noticed that the MANA MULTIPLER for support gems does not increase when the gem levels up. Am I right?

Looking forward to your replies! THANKS!!!