Hi, Gino. I don't believe that stairs with stringers are the way to go here. Instead, think of building 2 boxes, one of which sits on the other. You have much more design freedom to do things like make the bottom a step width wider all the way around. This ends up being much more visually pleasing than simple steps. Allowing the tread to overhang the box size by 3/4" on 3 sides will add to the visual appeal.
Rip 2x6's down to an actual 4-1/2" width and use these to build the outside frame of the boxes and when you put the 2x6's on top, you will have an even 6" per step. Don't forget to use pressure treated stock, galvanized or stainless deck screws and to use your dust mask when cutting pressure treated wood. Leave a nail width between your tread boards and dig out 6" down where the bottom box fits and replace the dirt with sharp stones to keep the wood from sitting in puddled water. This should be an easy and fun one-day project.