I agree with serpent. I love to plant things in odd numbers. So you could do five of one and five of another.
Or three, three and three.
I find that 10 plants of ten different types too busy. There is a lot to be said for clumps of the same providing variety yet interest. Ten of ten is way too busy to enjoy the form, shape and color of trees.
Personally I like three shorter kousa with taller acres in between the kousa clump. The Acers could be flanked on the other end by three flowering cherries. I find splashes of color with a anchoring clump of acer in the middle to be very soothing and comforting to the eyes. 3 kousa then 3 acer then 3 cherries would be pretty darn nice I think.
