1. How much weight should I give to choosing between DLSS Super Sampling and FSR? Is one massively better than the other, does it matter?
The consensus from what I've seen is that FSR4 is massively better than FSR3.x and AMD are now competitive, but it still lags behind DLSS overall.
Would I even need to use them at 1440p?
No, both cards can do native 1440p.
Do they provide future-proofing?
That's hard to answer. In theory, yes, because you can upscale to maintain decent frame rates as your card ages, but developers seem to be starting to "optimise" their games with the assumption of upscaling being used and that's a development I'd argue is diminishing the value-add it would otherwise have been.
2. When choosing a GPU model, prioritising quietness, which tier is going to be quieter, a low tier with low clocks and basic cooler, a mid tier with better cooler but higher clocks, or a top tier with massively better cooler but also much higher clocks? (and it must not have coil whine) (I paid extra for the 1080 Strix and it was money well spent)
The factory OC on most models is so tiny that the added heat/power is usually not significant when compared to the superior coolers. I don't know if this opinion is supported by the reviews, but my impression is that the AMD 9070 non-XT cards are pretty overbuilt for the level of power and you shouldn't have much trouble with them, but some of the 5070 coolers are really not great.
With a little undervolting and power limiting all the cards (even the basic ones) can be made to run quietly, but I'd definitely check reviews.
Would I personally pay extra from something like a Ventus (5070)? Yes. Would I pay extra over a Pulse (9070)? No, probably not. I'd be concerned about the quality of the overall cooling too, memory, VRM, GPU die, I wouldn't want 100C memory, for example and a backplate that actually has thermal pads and provides some cooling would be nice.
What is the current situation?
The nvidia drivers for the 5000 series have been pretty widely reported to be bad and I don't think nvidia has denied this, but there are also 5000 series owners that have had no issues. I've seen few reports of driver problems on the forums with the 9070/9070 XT, but as always, AMD has a reputation there and are going to be blamed quickly, even if the drivers are not responsible.
Personally, from the buying experience(s) of those on the forums, if you have strong doubts about the AMD drivers I would always suggest don't buy one. As I said, they're going to be the first thing that gets blamed and the card will get sent back and replaced with the nvidia one, so better/easier for ererybody to just go that way from the start.
. If you know how to undervolt, you could get this system to use less than 500W even lower than 450W at full load.