Focus on getting your Kael to 6*, not on another 5*. Leave Galek as he is, Kael is much better. Other future 6* champs include Skullcrusher, Frozen Banshee and Coldheart, although those last two are pretty specific and not that helpful yet in the beginning. You should also try to get a Warmaiden, she drops from campaign chapter 9 and will help a lot because of her AOE decrease defense ability. 

Thank you L9753! 

Agree with L9753, Kael to 60 to help farm your chicken plus he is great in Arena, early CB, and everywhere else really.

Spirithost will help in Arena, and dungeons. Here removing debuffs and increase atk is very helpful. May not need to go to 60, as you will end up with better champs down the line, I stopped at 50

F. Banshee and Skull will help your CB into NM and even UNM so those should go to 60, but in time.

Coldheart will help you Spider team and Fire Knight teams to lvl 20.

You need to use what champs you have, but dont spend too much resources on champs that wont help as you progress to higher levels in the game.

This is a great resource for help, and join a clan that will support you as well.

Is it just me or healing has no value in arena ? Should I use a healer or just use the steallife set ?

In arena healing can help if you're running a tanky team for defense for example ,  but speed and nuking plus accuracy for debuffers is what you shoul dfocus on for your offense