i've built a VB168 with Sensah (4 hoses), the 268 is the same infrastructure, so yes you can run mechanical. It's a major, major pain though, and the FD shifting will probably suck.
I've installed 5 er9 groups, they're wonderful. The app is awesome, adjustments are much easier than mechanical (especially FD, i hate mechanical FD adjustments). Together, we've only put 3-3.5k km on them though, so they might turn to shit, although i dont see why they would.
I really liked the 168, the 268 should only be better. I would do er9 on 268 with nice wheels (not less than 500-650$ range before shipping), gp5000 tyres, and you will have a wonderful bike.
On the lcr0x-d, it's a bit old now; i wouldnt buy a bike that maxes out at 28C, and T700 is on the ghetto side now.

That's a nice deal, best ER9-deal I can find right now on AliExpress is 644 USD. 105 DI2 is 1030 USD, including crankset, cassette, chain, and rotors.

In your Video you said, that there is a significant difference between this frame and a higher priced frame.
As someone who rides his Scott CR1 in the last 14 years and doesn’t ride a lot of different road bikes, I can not imagine what the difference is. Would it be possible to elaborate this?

Build done, except for missing bar tape. Er9, Magene p505, edge 45mm. Size 58 comes at 8.05 kg as you see it on the picture. Test ride is next.

Based on the hundreds of messages I received over the years, the typical viewer of my channel isn't looking for VeloBuild to be an equal alternative to one of the major brands. What they want is assurance their money won't be stolen, and that their collarbones won't be broken from a random catastrophic failure. Basically is the frame good enough all things considered. I try to keep my videos light-hearted and sensible. Save engineering and race opinions for the engineers and racers.

Confirmation bias and cognitive dissonance is human nature. Whether VeloBuild or Specialized, we all want to believe we've made the best purchase. No harm in that.