love that quilt! Check out Angela Walters, Krista Withers and Kylee Porter. Angela rarely uses rulers except on diagonal straight lines--I frankly try to avoid those! Krista would tell you to divide that negative space up into more manageable spaces and uses a mix of straight lines and curves. Kylee Porter does some awesome FMQ stuff that just seems to flow. You'll see a lot of Withers & Porters work on Pinterest to see what I mean. All 3 do pretty dense quilting.
I like your ideas with the exception of the clamshells in the background. I'd probably do something to divide up the space and use some contrasts (i.e. straight lines next to spirals, etc). PLEASE post a picture when you are finished quilting!