WEll 1st of all, you don't really need our permission if you feel you want/can do commissions. It's your choice and you have a right to open a commission thread if you want. Usually, the fan art community here is very open to every kind of art and I've yet to see one commission thread go unanswered or without interest

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Now for your sketch, 1st thign I notice is the lack of eyes. To me, eyes are an important feature of the face so perhaps working to get some good ones with details would really liven up your sketches ^_^.
Oh and if you plan on sticking with pencil, might I suggest adding some pencil shading to your work, it gives pieces a lengthier and wholesome feel to them.
Except for that, it's really nice

. Details and proportions are well done and pose is good(but since you plan on doing portraits I guess poses aren't that important except the angle of the face). Your stuff seems quite commission-worthy if you really want my opinion.
Note that I'm not really an artist, nor a good art critic so maybe other people have opinions.
Good job! ^_^
Kay