My FTP is waaaaay lower than Dallas, and i wouldn't run a 52 on a TT bike. But obviously, if you're not going to ride it on the flat, then it gets complicated. There are useful online tools to figure out, based on cadence, gearing and so on, the speeds at which you can ride. I can tell you that i dislike high cadences, so at 80-85 cadence, i dont want to be doing tempo in the smallest cog on the flat, because it means i spin out as soon as i start pushing, which sucks. Also, the smallest cog should always be an emergency cog, not a "i'll be doing my hard efforts in that cog".

On crank arms, be careful, you might be throwing good money after bad. I'd get pedal based power meter and shorter cranks. I'd get 165mm, now that they're cheap from China. If you plot it trigonometric-ally (?) you see how big of an impact crank length has on how high your knees go up into your chest in TT position. So it's not a marketing trick to sell more bikes. It's just objectively more comfortable to be horizontal with short cranks. And sell your 172.5mm rig before nobody wants it

You have to figure out what would be your expected power output for the key sections of the course and select chainring size accordingly.
It really depends on your power output, cadence and actual course (rolling, long climbs, consistent shallow gradient etc.). For example, I have FTP around 350-365, mid season weight 72-75 kg and my TT bike has 1x12 setup with 58T (oval) front and 11-34 rear and during tempo rides (260-290 Watts@90 rpm) I slip into smaller half of the cassette. If I model the actual race scenario, I will push closer to my threshold and I will be even further down the smaller cogs which will cost quite some watts, you have to be closer to the middle of the cassette during your main effort. In this case, I need a bigger chainring, 60T or 62T.

IMHO, unless you have long very shallow gradient or very long stretches of flat terrain between steep climbs, 1.5-2.5 kg lighter road bike would be more beneficial for such event.

Keep us posted, I'm in Europe too, and agree. When i looked at it, assuming the frame allows, my ccl was i'd do mech disc, because the ride rever hydro are super expensive. I have mech discs on my gravel bike, they do work. Hydro is better, but i wouldnt be descending hairpins on a TT bike.
Also, from a traveling perspective for races, sram wireless + cable actuated brakes should be easier to live with than hydro hoses. And Hambini in the last nero show podcast said he had to empty his hoses from hydro fluid several times while taking planes in Europe. I doubt he made that up.

I’m running these RideRever hydraulics on my Velobuild VB-TT. They’re good, haven’t used the SRAM Hydro’s to compare to. But once upon a time these RiderRevers came stock on Cervelo TT bikes.

I am thinking of the same in the future
I would try these- https://www.riderever.com/product/5/17/28
paired with Sram rival axs and blips.
still on fence about frame as i try and do UCI nationals and gran fondo TTs - unless i can get one that is very close to original and slap a UCI sticker on it!