I built (okay, I still need to bleed the brakes and put in sealant but it's 95% complete) a 696 for the same purpose and also had the idea to use Lighterpack. Here's my build for inspiration. Note that weight might be ~200g off because I got too impatient and installed the components before weighing them like the tires so I'm using the retail weight.
Hope it inspires you. Also note that I took a very expensive custom paint. Yours might be a lot less.
https://lighterpack.com/r/vejgggMy 2cts about the wheel questions:
Centerlock 1000%. Fuck 6bolt. And get the HG tool lock, not BB lock
The hub depends on the cassette you will get, not the groupset. You can get microspline or XD cassettes to run with LTWOO, it's up to you. It just needs to be compatible with the cassette.
I sourced both of my wheelsets on the used market, I'm happy about both and might upgrade to carbon later. Anything with DTSwiss 350 hubs is good imo. I also considered Carbonda wheels but I changed my mind when I was told shipping the wheels would be extra.
Also my opinion, as much as I'm excited for LTWOO hydraulic unless you find them at MSRP I wouldn't bother. I bought my GRX groupset before it was anounced but I don't regret it. There's a good chance you can find GRX new (mine was stripped from a new bike) for about the same price as LTWOO if not cheaper.