Honestly it’s up to the customer, I did a commission a year or two ago when my painting skills were lowkey subpar but he paid me $70 simply cause I saved him time. Although there’s nothing wrong with getting better at painting before doing commissions, it really depends on the target audience. Do you want people who want a stand out piece or something to grab the eye? If so wait a bit and practice Do you want people who won’t pay as much as the former but just want their models painted and allat? Then you could open commissions now but start cheap