I think you’ve decided on a “new bike”. Problem is, you are starting from an already very good bike that came with genuinely rubbish wheels. Forget number of gears, the wheels on the CAAD8 have always been a weak spot and need replacing.
Upgrade to a set of Ksyrium Elites and the bike will be transformed (and half a kilo lighter). Upgrade to a carbon seatpost and bars, and again the feel will be transformed. Upgrade to 11 speed 105 and it may shift and brake a little bit better. You may not like the feel of the hoods on the shifters as much.
You have to raise your budget quite a bit to make significant improvements. The CAAD8 frame is that good (OK it’s welds are rough, but the tubing and geometry are spot on.).
As for fit, try a 90 mm stem instead of the stock 100 mm. You are the same height as Teen1, and I steal borrow his 54 CAAD8 (with 90 mm stem) and swap to a longer stem for my own use. I also swap to a carbon seatpost with my preferred saddle.