I'm glad you found my swale posts at TenthAcreFarm.com useful. :) The swale referenced in my articles was dug into solid clay, and as mentioned above, it works because the slope allows the water to continue draining downhill and away from the house when the system fills up and the water can't infiltrate the clay. This is essential for the system to work. Gravity is your friend.
Sowing with daikons or broadforking is a good idea. You could also puncture the clay throughout the trench with a digging fork. Then sprinkle some compost throughout to fill those holes, which provides food and oxygen to attract soil organisms to work on that clay layer, soften it, and allow deeper infiltration of the water.
I'm glad you're making sure to plan an overflow. If your swale trench fills up, where will the water go? Where do you want it to go? Can you direct it into a rain garden (like I did in my system), into a diversion trench directed to another garden bed, or simply away from the house?
Concerns: The uphill planting berm closest to the house might not be a great idea. You want to encourage water to run away from the house, and a thick berm like this close to the house might collect more moisture and insects than you want. 15 feet away from the house should be fine as long as gravity is your friend and the trench is correctly on contour.
As far as filling the trench, I found pluses and minuses to each type of material. For function, gravel and large rocks topped with wood chips (that you can see in my TenthAcreFarm.com article photos) worked fantastic. My swale functioned like a dream for about five years until I moved. But I had figured the trench would need to be dug out occasionally (every 8-10 years?) to aerate the clay bed and to be sure the material in the trench was not too compacted to do its job. Digging out gravel and rocks is not that fun.
Alternatively, I worry about decomposing wood chips holding too much water. By the time I moved, I wondered if that was causing a mosquito issue. If the trench was only wood chips, then you could dig it out every year, use that compost in the garden, and refill with new chips. You could also think about planting that trench with deep rooted, native rain garden wildflowers (bee balm, coneflower, blazing star, etc.). They will encourage a good soil biology that would continue to decompact the clay for you and soak up any water that might otherwise sit there if the clay barrier issue isn't worked out. Also, flowers = pretty landscaping!
