I just finished the border! As suggested by the big majority in this forum, I've used the green polka dot fabric. I quite like how it turned out! The colours in the picture are not completely accurate as we're having night right now and it would probably look better if I'd take a picture in daylight, but I didn't want to wait until tomorrow!
This quilt top is quite experimental as I didn't know at all if the twister pattern would work with hand piecing... I was prepared to have it disintegrate once I start cutting, but it did hold!
Now the big question is how to quilt it... I've seen a quilt with concentric circles somewhere on the web and liked the simplicity of it very much. What about starting with a quarter circle in one of the corners and then do bigger and bigger circles all over the pinwheel part?