23 is a good level to set yourself up at
I'm lvl 70 now, but i still use my lvl 22 (use to be 23) mech when there are few players online
If you create a mech that's higher level than 23 though, you will start facing the next rare item torso (Gladiator) and will struggle against it. So it's best for early levels to try stay below level 23 till you can start building higher up lvl mechs
Don't waste money building a mech where your torso will be outmatched by a higher level torso
This is the same for all levels where you have to try not encounter the next level rare item torso.
Apart from that it's all down to preference
I have mechs at level 22, 33 and 53.