Your design looks great! Perhaps x axis will be a bit slow due to the threaded rod (do not use my grbl configuration for the speed, that would be too fast for a threaded rod). It looks like you have used some old printer parts.
I had my personal fight with grbl almost a year ago. I added some more instructions, make sure you check them. The links provided will explain everything better than I would do. If you decide to use limit switches, you will have to configure that also in grbl.