I released a robot who I ordered to get grocery on my way to museum for GNR q. It aggroed a Super mutant brute and a master. Game over pretty quickly (just lvl 7). Masters seem kinda tough, how common are they?

It seems monsters getting tougher at increase of lvl, lots of mutants, raiders with flamer, even met a Gutsy not far from Megaton which was quite a challenge (had to run around a big wall taking cover) Do monsters scale in lvl or am I just at the wrong places? Thanks.

Sounds like you were just in the wrong places + generally unlucky. Also, as you increase in level you will start to find tougher enemies. I can't remember the exact cut off but for exemple, around levels 1-4 you might only find regular Super Mutants, at levels 5-8 you'll find Super Mutant Brutes and at levels 9+ you'll find Super Mutant Master's. And sometimes the enemies are static, meaning no matter what level you are the enemy generated will always be a Master.

If you have Broken Steel, the Masters are only the beginning of your worries. I've seen Overlords as early as level 10 or 11.

I HATE i repete HATE overlords more than albino radscorpions.

I don't mind the overlords so much. Yeah they're bullet sponges and all, but I kick ass with the Paralyzing Palm. I can take down one overlord and one master with a full magazine from Eugene. It's the reavers that own me all day long.

I'm not sure how to take down the brutes effective, when using i.e. hunting rifle or pistol one full vat barely does dmg unless crits. Should I aim on the mini gun or some other part? And if I'm far away many shots will miss.

If you're having troubles killing them, definitely shoot their weapons first. Once they are weaponless, a combat shotgun to the face will down them in a couple of blasts.