Everyone needs practice, either to learn or keep their skills in check, or to adapt to something new in their art.
As for whether your art is good enough for commissions, I would say so, but what you really ought to be asking (yourself anyways) is how much you want to charge, and then weigh that with your skill, ability, time it will take you to complete a commission, etc, so you find a price range that is fair to you and the customer, or a price range that ensures you get the profit you deserve for the level of work you're putting in.
I do commissions and you can look at my journals for it to give you an example of how I charge, not that my way is right or wrong.
Whether your work is good enough commissions...depends on if you have enough people willing to buy your work. Reputation, I think. I'm not sure if skill has much to do with it.
All these characters are from WoW.
Also: Good enough for commissions yet?