I've installed my power meter now, I used this bottom bracket: https://www.aliexpress.us/item/2251832835484740.html

and it worked well! The only thing I haven't diagnosed yet is that I have tried to use my Ultegra 11 speed chainrings with the crank, but the spacing between the two chainrings is wide enough that the chain can fall in the middle. I need to take it apart and see if I installed something incorrectly, or maybe the flanges that the chainrings mount to are thicker on the Magene vs. Shimano crank arms?

100%, at this point the bike is going to just sit there until I can find a shim and get the motivation to spend a few hours undoing and redoing everything

That's a good point--now that I've done some initial fit testing I should be able to cut it down quite a bit

Finally figured it out--silly mistake  .

1. Unscrew the bolt holding the front derailleur housing stop, you'll need to hold the back side of the "spring clip" by putting your finger into the frame so it doesn't spin freely.
2. Once the bolt is loose, remove the housing stop and retrieve the "spring clip" that fell into the bottom bracket area
3. Route the front derailleur housing out of the opening in the frame
4. Thread the spring clip back onto the bolt--only screw on enough to get the thread started
5. Put the assembly on the end of the front derailleur housing
6. Push the assembly back into the opening as far as you can. It won't fully seat because the spring clip needs to be pushed in far enough to "spring" into the opening in the frame. Use an allen/hex wrench to push the bolt (with the spring clip barely threaded on the end) into the frame--pushing the bolt directly will push the spring clip into the frame enough that it will actually grab
7. Screw the bolt until the front derailleur housing step is secured. Note you may need to put your finger on the spring clip so it doesn't rotate

Hopefully that description plus the photos makes it easier for the next person! I routed all three cables up through the down tube--front derailleur in the center (with foam), then rear brake on the brake side and read derailleur housing on the derailleur side. Everything routed through the headset pretty easily.

My OG-EVKIN stem is really tight on the steerer tube, I had to pry it open a bit with a flat head screwdriver to get it to fit (my aluminum stem had no issues fitting, so it seems like a OG-EVKIN stem issue, not the fork steerer tube issue).

Bike is ~15.4lbs so far, need the chain, pedals, bar tape, and seat yet. I'm not looking forward to routing the derailleur/brake lines through the handlebars or bleeding brakes--I may get the bike set up on my trainer and do a few bike fit tests before everything is completed to try and make sure the handlebar height is in the ballpark before routing everything. I plan on leaving a good bit of steerer tube free to make sure I can adjust more as needed down the road.

Second photo post--some quick early photos trying to take shots inside the frame. I know an elementary level of carbon--I think this is using the air bladder style inside instead of the EPS that newer/nicer frames use? It definitely doesn't look as nice as other internal shots I've seen, but I don't know if it's an unsafe level?

Small update--UPS tracking shows the package was picked up in Hong Kong with a weight of 4.2kg, and it has an estimated delivery date of tomorrow  . I'm not getting my hopes up that it will actually make it by then since HK -> USA is a long trip! but I do live close to a major UPS hub so it's possible it will be air shipped directly to my city.

The power meter is also in my state! So it should probably be delivered by tomorrow as well.

They updated it with a number that looks like a tracking number but has no info yet. I'll be curious how long the shipment takes