>>535372906
7 is a good bang for the buck place to stop.
The reason why you would even want level 7 in those skills is in case the game challenge you with om solo runs or something. Otherwise you could even stay at level 1.
But level 7 gives you that sense of completion: You have done what you could to complete the agent in a reasonable manner.
Going higher than level 7 for mostly useless skills is ludicrous though, and a waste of resources.