Nice build! I built one earlier this year and love it! It took me a little while to get used to the aero aspect of the frame. Can get pushed around in a cross wind. Good thing i didn't go for the 50mm deep wheelset....lol!
As far as setup goes i used all the tools at my disposal i.e string, goniometer and video of myself riding it. I started with a 120mm stem and the bike felt great! I went for a few short rides around 15 miles and it's the most comfortable i ever felt on a road bike. Then i went for a 50 miler and man, my back was killing me at the end. I felt too stretched out, like i was reaching for the handlebars for the last 15 miles. Since then i went to a 110mm stem and that's about as perfect as i can get. Feel really good on the bike and no more back pain regardless of the miles. It takes time to get used to a bike and put some miles on it before you can really dial it in
Just for the record i am 6'1" tall 200lbs with a 32-33 inseam. The 56cm frame fits me well and i have always like sloping top tubes. I feel like i'm actually "in" the bike. Pictured below during setup:
