Yes.
We can provide a more nuanced answer here (as in, what OpenWrt calls mac80211 is a backport (suite) of the mac80211 stack and its drivers to older kernels, in case of 23.05.x kernel v6.1 based kernel wireless drivers for the v5.15 kernel used by OpenWrt - and the first link conflates mac80211/ cfg80211 based drivers with legacy ones), but those are details - and none of that matters for the contemporary chipsets/ drivers you can (should, with OpenWrt in mind) buy today.
Yes, a good experience is only the combination of acceptable throughputs and decent latencies.
Right now, we don't have any supported wifi7/ 802.11be routers yet (filogic 880 and corresponding wireless cards for OpenWrt aren't that far away though; ipq53xx/ ipq957x is already on the market, but its path towards OpenWrt will be much longer).
802.11ac devices are fine if you already own them or can get them for a bargain on the used markets, there's no reason at all to replace them - but at the same time it does not really make sense to buy them (new) anymore either, as we have a solid OpenWrt supported selection of mt7621+mt7915DBDC, mt7622bv+mt7915, filogic 820/830 and ipq807x (and hopefully soon ipq60xx) devices for reasonable prices (often less than their wifi5/ 802.11ac predecessors) on the market. Yes, the more modern devices might need snapshot builds for now and may be harder to flash, but you get better hardware in return for your efforts.
Yes. mt76 might be slightly easier to profit from work on this.
MT7976AN is the 5/ 6 GHz phy frontend of the Mediatek mt7916 (wifi6/ wifi6e, 802.11ax) chipset, supported by mt76 - supporting 4 antennas/ 4 rx/ tx chains.
Qualcomm QCN5054 is the 5 GHz wireless chipset (QC5024 would be the 2.4 GHz counterpart, QCN9074 the 6 GHz one) from Qualcomm (wifi6, 802.11ax), supported by ath11k - supporting 4 antennas/ 4 rx/ tx chains.