It is simplest to Home Towards Minimum. But that assumes your limit switches are on that side of the various Axis. You can put the origin anywhere you want. But assuming you can home towards Minimum, it is most straight forward to make the home position 0. (Some people do put (0,0) at the center of the bed and have a plus and minus number for the limits of the X & Y axis)

If you can do what I said up above, you would change:

#define X_MAX_POS 150
#define Y_MAX_POS 150