The smallest individual cog that can be spaced in or out (for chainline) on an mtb hub is 12T, the front sprocket would need to be a 28T (on a 24" wheel)
You can use the 11T of an MTB/road cassette but it would have to sit next to the lockring, like it does on a cassette, this may give an odd chainline, then you can use a 25T at the front. I used 30T and 13T at the back on my 24 and found it fine for skateparks and dirt
Hope this helps