congrats! very nice bike, always liked that red-black colorway.
also a di2 guy, so no input on RED, but to your other points, if you're not riding serious off-road i like the various sp-connect mounts better than quad-lock for a creo. if you're a paranoid type there's a version with a little bit of shock absorbing material (the MTB version) that isn't too bulky.
https://sp-connect.com/collections/bicycle
the s-works power saddle is nice. i upgraded mine (it's what came on my s-works aethos) to the s-works romin evo with mirror. there are three great mirror saddles in the same range, power, romin, phenom. depends on the shape of your butt and legs, but i like the mirror saddles a lot. i don't like the hover bars since i prefer more drop and a more aero position, so i'd change those out too. i went with the alpinist cockpit but that's personal preference.
i wouldn't ride a creo on the road with 510s, they're incredibly bulky and heavy and sweaty. maybe you're riding gravel or dirt mostly? the s-works creo is very well specified, few or no "needed" changes. the terra wheels are fantastic. i'd add a SWAT mount for a garmin varia, the garmin varia itself, clipless pedals (unless you're riding dirt), the sp-connect for your phone, a bottle cage, and go tubeless unless you only ride the bike very rarely.