...but I worry about the image quality maybe not being adequate for sim racing, I have no idea in that regard.
How does 1440p look like on 32" in regards to sim racing?
It's fine. You could even race with a 40" monitor at 1920x1080 and it wouldn't affect racing. Sure, the image won't look as nice/clean, but in terms of pure racing, it won't have any affect. Plus, all sorts of forms of anti-aliasing, post-process anti-aliasing, DLDSR (stay away from non-DL DSR), low pixel density isn't that big of a problem. Of course, a natively, high pixel density screen is nicer but it's barely an issue during gaming / racing.
1440p on 32" 16:9 looks good. I had triple 1440p 27" prior to triple 1440p 32" (and then, after getting a Pimax VR headset, I moved to single 38" 24:10 ultrawide and now a single 45" 21:9 ultrawide), and the pixel density loss is minor. After 2 laps, you'll never think about it again.
I'd personally aim for 240 Hz. There are so many moments where framerates are well above 144 or 165 fps. Depending on amount of opponents, how many opponents are near you (like at the start of a race), different conditions, hotlapping alone (or playing online with, sometimes, very little opponents), different games altogether, different in-game gfx settings, different amounts & types of AA, etc. It all depends. Also, thanks to G-Sync / Freesync, you'll always have a nicely synced, fluid image all the way up to 240 fps/Hz regardless of whether the framerate is at, say, 90 fps, then goes up to 210 fps, then 135, then 230, etc. Rather than capping out at, say, 165 Hz. It's not a must though but, me, personally, I'd choose 240 Hz 1440p over 144 or 165 Hz 4k; the fluidity combined with the large increase in motion clarity way outweighs a slighly cleaner/sharper image which can, partially, be compensated for on the lower resolution monitor anyways with things like AA, DLDSR (I don't think DLDSR is available for triples), etc.
Well, tough decision. 4k is definitely more future proof
I'm not sure what you consider "future proof" when it comes to monitors but if you want to "future proof", you'd be looking at 240 Hz, 1440p minimum, 32", OLED, HDR. If that's the case, then I say wait a little longer as there should be quite a few awesome 32" OLED, 240 Hz monitors coming out in the next year or so.
If you don't want to wait, then Asus just released their Asus ROG Swift OLED PG32UCDM which will give you the best of everything: 32" (16:9), 4k, 240 Hz, OLED, HDR. It'll probably cost an arm and a leg though. If OLED is too expensive, then your other option is a mini-LED with lots - meaning over 1000 - dimming zones such as the Samsung Odyssey Neo G7: 32" (16:9), 4k, 240 Hz, mini-LED w/ 1200 dimming zones HDR. A sweet spot maybe is the other Samsung Odyssey Neo G7 model. It's also 32" (16:9), 4k, mini-LED w/ 1200 dimming zones, but it's 165 Hz instead of 240 Hz. That might be a great sweet spot in terms of price and future proofing.