When I play Mtt, do I always look at the blinds above 20 and am I safer or should I take more chances? I am always in doubt whether it is worth the risk of playing the reasonable hands giving limp or mini raise so as not to compromise my stack.

I played more loose AJ as in the example below, but I paid high in the River

A screenshot is nothing without context.

How did the hand play out?

In this context I am showing for being above 20 blinds I tend to play more open, I wonder how many blinds would be a healthy stack to work on mtt?

I look for feedback on blinds, AJ hands would be ideal to shove down 10blinds or 20 how much blinds I could work.

It's tough to say. I think AJ is generally a very overvalued hand by most players. I would need to look at position, opposing player tendencies and stacks, who acted and what they did, what stage of the tournament you are in, etc. . . . Late position with a limper or two I don't mind a shove. Early position I might if I think I will be heads up for 10BBs, otherwise I would not. Lot of variables.

mtt, blind 25/50
i mid table/ vilain smalblind.
My Stacks: 2450
Vilain: 3050
I 3bet pre flop/ cbet 150 flop/ Vilain raise my cbet 300/ turn check, check/ river vilain raise 750. I call.

Overall, I'm in doubt as to how much my stack is good and how much blind to get to work.

How big was you 3-bet? So you limped then 3-bet the SB, that seems ambitious with AJ. I don't mind the call of the min raise on the flop but the c-bet is too small to gain a info. By making such a small c-bet you put your self in a bad spot on the river.