My wife is a former SES that reverted back to a GS-15 position to stay out of DC.
What they are offering is a "ladder" GS 9 to 11 and perhaps beyond. Not bad.
As far as "steps" go, they are generally negotiable. If you are getting a ladder to an 11 in a year I would not make the "step" a deal breaker. Here are the rates:
https://www.generalschedule.org/GS-9
Depending on your degree, the scale slides up. Make sure you understand what your degree means for pay: My wife is an engineer and hr salary is a a level beyond the general pay scale.
All that said, will you be in the Pentagon or DC/Arlington in general? It matters.
Good luck! Oh, use and abuse TSP.