Hi. I will do my best on these 2 questions for you. 

1) I would use ground and "to step on", not "stepping". I have flown a lot and never heard it said this way, although it is not wrong. What I have heard is "it feels great to be on the ground again". Also, I used "great" to replace "really good". Really good is not wrong, but using a better word like "great" or "wonderful" in place of really good typically sounds better.

2)This is a question that highlights English being weird. Both are correct. You can say you ran on the grass or in the grass. I would say in normal speech I would say something like:

    "I like to run in grass/sand"

    "We ran on the grass rather than the pavement"

Hope this helps!