What should I have and by when

New to Xcom, somehow surviving my first run in legendary ironman up to September.

I currently have Full magnetic weapons, first universal armour upgrade and bluescreen.

It was hard but managable up until this mission where Andromedons start to show up, accompanied with Mutons. My current damage is just not enough to take out a 4 man pod in 1 turn let along sometimes I have to trigger 2 and realistically my soldiers miss.

If I don't then the next turn Mutons throw grenades and Andromedons fire rockets.

Am I just underpowered and DESPERATELY need plasma or is trading damage just unavoidable and I need to a med-center.