Okay I see. You are talking about two things, what we call CAD and CAM. CAD is actually designing the part, CAM is programming the tool paths.
estlcam is only for CAM, Fusion 360 does Both but is extremely powerful and very intimidating on the CAM side the CAD side is pretty straight forward.
You can still use easel for both your CAD and CAM. Once you have your design you can click Machine-Advanced-generate gcode-export gcode. That file can be used on any firmware (as far as I can tell), so you could use the LCD or Repetier.
I am not sure how stable the grbl firmware for ramps is at this point. last year is was not. if you are having a difficult time with CAD and CAM firmware is much much more difficult to try and diagnose. The CAM side I feel I have covered in some very basic to medium difficulties covered here on the site in the Info page, but CAD you might want to check out some of Maker Muses tutorials, He has them broken down very well.
If you really do not want to learn a different system, why not just get a grbl based board? I have one listed on the firmware page and there are dozens more to choose from. My machine doesn’t care what board runs it in any way. My suggestion is stay very far away from the newest versions of the Ramps imports.