I'm also building a gravel bike with similar budget and component range. I've only just begun ordering parts and haven't received anything so I can't share experience with quality or build experience -- only my research so far.

Here's my input on your questions.

1. Yes, carbon wheels are great for gravel. I don't think you're going to notice the choice of spokes. There are common complaints of poor water resistance with the stock Elitewheels hubs (RD05, RD07, ... RD13, etc.). They are also REALLY loud hubs. Another thing to consider with Elitewheels is they take an INCREDIBLY long time to ship after your order. 10 -- 12 weeks is common. Tracevelo on Youtube has some very informative reviews and breakdowns of these wheels if you have concerns with the stock hubs or anything else. Takeaway is positive.

2. I doubt you'll feel a difference with lighter/upgraded spokes (though more spokes is better with gravel riding I hear). I might consider getting a wider (hopefully tubeless) tire if you'll be riding dirt or gravel roads. 19.5mm inner width is plenty wide. You can actually fit as wide of a tire as you want in general. Its actually the reverse that's not true (can't fit narrow tires on wider rims). Here's a good article I found on the topic of rim inner width vs tire width: https://www.renehersecycles.com/myth-18-wide-tires-need-wide-rims/

Side note, I also went with Elitewheels but I selected their gravel specific wheelset, at 35mm deep x 32mm wide, tubeless ready:https://www.aliexpress.com/item/33003076757.html?spm=a2g0s.9042311.0.0.27424c4dUfrqoq
I'm planning to fit at least 37mm wide tires for more comfort, might go as wide as 40mm. These wheels have an ID of 22mm so should fit tires from 37 to 60mm+ tires (not that I ever intend to go that big).

3. You need to select a bottom bracket that fits both your frame (matching type AND shell width) and your chosen crankset (matching axle diameter). Both frames you linked to (the Winspace G2, and the Carbonda CFR696) use BSA with a shell width of 68mm, which is standard for road bikes. (Mountain bikes with BSA usually have a wider shell of 73mm.) Note, the BSA standard actually has an inner diameter of between 33.6 and 33.9 mm, which is larger than the Hallowtech 2 diameter crankset you have selected (24mm). HOWEVER you can buy adapters (sleeves) to mate narrower axle diameters to a standard BSA BB, or buy an "all-in-one" BSA BB with a non-standard inner diameter, like 24mm. I think most people do the latter. Zrace makes a 24mm inner diameter BSA BB that should work fine with your frame and the Zrace Hardrock crank: https://www.aliexpress.com/item/1005001500906036.html?spm=a2g0o.productlist.0.0.4c0b5535biScWn&algo_pvid=08cef7ab-fae7-45fc-8173-ae3bd297072b&algo_exp_id=08cef7ab-fae7-45fc-8173-ae3bd297072b-9&pdp_ext_f=%7B%22sku_id%22%3A%2212000016362458412%22%7D

4. 100x12mm and 142x12mm is pretty standard for road frame thru axles. Both of the frames you linked have this size, although it looks like you can optionally specify 100x15mm for the fork on the CFR696. You want 100x12mm to match the wheels.

5. I'm buying the same brakes and Sensah shift leavers, so I'll let you know how they perform! I think I saw on your spreadsheet you are swapping out the pads with Shimano resin brake pads and you have compressionless brake housings. I also read both of those things will improve these brakes. I'm doing both as well. Make sure you have adapters for the brakes to fit 160mm rotors.

One last thing -- I think the Zrace rotors you have there are six bolt. Most of the Elitewheel hubs are Centrelock, so you'd need an adapter like this: https://www.aliexpress.com/item/4000260123765.html?spm=a2g0o.productlist.0.0.4add65d6pLuy7I&algo_pvid=69da709b-8071-4a13-b087-0cb14ef89876&algo_exp_id=69da709b-8071-4a13-b087-0cb14ef89876-5&pdp_ext_f=%7B%22sku_id%22%3A%2210000001057121839%22%7D

1. Are you set on this frame? It is very expensive as far as Chinese frames go. It is new and unproven, but likely fine. And personally I find it unattractive with the super dropped chain stays, 'mullet' paint job, and countless mounting bolts.

2. Nothing wrong with saving money using Sensah. However, 50/34 with 11-32 may not be enough gear for touring and I've seen some crazy steep climbs in Thailand too.

3. For handlebar I'd suggest looking at the FSA Adventure, same price range but it's got a nice flair in the drops.

4. I would probably pick a different tire. The GP5K is great for speed but I think there are better options for endurance/touring.