In my experience, people can say sentences like:
"How much guitar do you play a day?"
"How much do you play guitar a day?"
Do you think they are interchangeable? I think so.
How much guitar.... is grammatical. I think it's analogous to this transitive:
How much food do you eat each day?
You eat how much food per day?
How much distance do you travel each day?
How much tennis do you play each week?
How much beer do you brew each day?
How much crime do you see each year?
P.S. Does the question How much guitar do you play each week? mean "How often do you play?"
Not necessarily. The person you've asked that question could reply "10 hours a week" or "every day".
P.P.S. In the comment I've given an attestation of a different version of the question: a fan asks a guitarist how much guitar he plays on a particular album. There the phrase means, "How much of the guitar playing on the album saw you on the guitar? What portion of it was you?"
And here's another with the same meaning as OP's original example:
How much piano do you play before a concert?