I'm not sure how to respond to this question :-) How one chooses to organize their own garden is pretty much a personal matter so the groupings you contemplate are very subjective. Rather than evaluating your 'clusters', I'd prefer to see how all these trees are grouped in the landscape and what other plants accompany them. Do you have sufficient room for 27 different JM's, some of which will get to be of a pretty good size, either with regards to heigh or spread? What else will be planted?

Some of your combos seem to include a rather wide range of heights/habits, so the initial planting could look very different once some time has passed and the trees become established.

I think there is room - although the groupings will be rather maple-centric. The other plantings will be mainly conifers.

I tend to mix my japanese maples in with my conifers. Some selections like Shishigashira are nice by there self since it is so unique.