Now I'm looking at this arrangement. I'll move the blocks around a bit before joining them all for a better color distribution. What do you think? And what suggestions would you have for quilting, if you like this? Do you think it needs some additions?

How about some colorful prairie points sewn into the seams between the blocks? (As long as you don't plan to machine quilt it, because loose triangles would be a pain if machine quilting.)

Run some of the blocks with the seam going side to side instead of up and down for a little extra interest? I do think it needs something else. That is a lot of background. Maybe a narrow inner border in black. I've seen some bright fabric with multicolored open circles in the novelty section of my LQS might be perfect for outer border. I believe I've seen it with backgrounds in red, blue, and lime green.

What about a large all-over swirl panto?

Or maybe this one?

I like that one. Maybe a line of vertical sashing between the two rows?

Watson

I like your second layout best, too. Now the background doesn't over dominate so much.

I like the first one better. Actually, I like them both, but the backgrounds in the second column in the second layout look so similar, it stands out.
As far as quilting, your layout gives you so much opportunity for fun fills. I would look at Angela Walters, Green Fairy, or Leah Day's sites for inspiration. You could also do channel quilting.
Please post the finished product!!!

I love the one where you 'cut' the blocks in 4 the best, but the one where you 'cut' them in half works too.

Would it be okay if I suggested your block to my guild for a block of the month?

Sure. I'd love to see what they do with it.