Frostbolt Scion, Please Help

So I am what you would call a noob when it comes to PoE and I could use all the help I can get. I should note too that I am pretty poor on PoE too.

For offense I wanted a high crit and freeze chance to freeze lock as much possible, including bosses. For defense I was going for max res (including chaos), decent life, decent shield, and high evasion to give my shield a chance to recharge.

Right now I am doing 79k DPS with max charges and onslaught, which is awesome but without my charges I drop to 56k and I am still not freezing most bosses. On the defensive side I am squishy to say the least. I don't have near enough life and I am contemplating if energy shield is a waste of time since I have no way to get it back up once I lose it.

CURRENT PASSIVE TREE (I'm probably doing this wrong)
https://www.pathofexile.com/passive-skill-tree/AAAABAABAAVCBx4J2Q18DkgPxBEPES0RLxFQEZYW8xdUHNwdTyBZIoEi9CY8KwosnC0fLagvnTW5Olg7DTt8PEtBlkWdRnFJT0lRSbFMLUyzUilTUlPUVcZV4FZKWBdYWl3yZJ1odGwLbRl7w3yDf8aC5IMJhTKKr42CjjyPGo_6kBGTJ5SglS6XLZrgnqGfAaEvoj6io6crq7qsmK6zsZC0DLfWuMq5k7yqvoC-ir68wcXDCcpGytPQH9D10eTXz9hN2mLbWeKt6rrrY-vu6_XviO_r8NXyHfk3-eg=

MY GEAR


So here are my questions:
1. How does a spell caster survive without the ability to leech or get massive amounts of armor/life?
2. How do I freeze the big boys more often?
3. What can I do to improve my clear speeds?
4. What can I do to augment my character with support gems in unused links with things such as cast when damage taken?
5. Do you see any waste or better paths for my skill tree?

Thanks in advance and if you have input on even just one question, I'd still appreciate it!