You can ask your opponent if he accept that you play full extremis chamber because you only want them and don't want to waste the look of the army with 10 liberators. Maybe he'll accept. People don't always follow blindfully the book and are ok with some little twist.
If you want to "play by the rules", maybe 2 units of 5 judicator with bow can be ok, being the vanguard of your army.
For the rest... well, all the models of the extremis chamber are VERY brutal. You will play a steamroller who destroy the opponent with brute force.
the two lord celestant are very good, but i think that, if you play the general, at least give him the biggest dragoon

he is very powerful and have good utility, boosting the drakesworn templars.
For the "troops", the warscroll battalion are very good, so you can play with them, or without. Actually, everything is very good with the chamber. So you can really play anything you want.
The first battalion is the lightning echelon, with two units of guys with spear and two with crossbow. It give them a sweet 2+ save (with reroll of 1) against shooting, and, one per game when you charge, you deal one mortal wound per dracoth who charged, and then you can pile-in and charge AGAIN, trough ennemy models.
the second is the thunderwave, with the guys with hammer and axes. When a ennemy model flee, you can roll a dice, and on 5+, you kill another one. And one per battle, you can make them attack a second time.
So, i think a guy on dragoon and two boxes of guys on drake could be a good start.