HC beginner need help on gems

Hi guys, I'm a new Hardcore player, currently playing on Tempest League.
I'm a level 51 Scion and only using Explosive Arrow + Fire Pen + GMP + Slow Proj.
I also use Decoy Totem for more survivability. I also have Blood Magic from my skill tree.

Since I'm going to Merciless soon, I need help for more gems setup.

1. What else should I use or link??
2. Should I keep using Decoy Totem??
3. Should I use Flammability??
4. What should I link with CWDT?
5. How can I regan HP faster?

Thanks for the help :D