u can refer to the first post enthusiast gaming reco, and swap out ur gpu as desired. as long as u have a relatively modern dedicated gpu, u should good for 4 monitor support.
9700x performs well in a vacuum, but in reality where there are other competing products, the premium u pay for it is not justified for the performance on offer. for eg, u can get the 7700 non x for quite a bit cheaper while still keeping 95% of the performance of a 9700x.
it kinda depends on what ur gonna be running. x3d is good for games yes, but it only makes sense when ur gunning for max fps, like competitive shooters where responsiveness is critical. otherwise, most modern processors will deliver adequate performance for a much lower price, especially if ur gaming setup causes u to be gpu limited first before cpu limited, eg when u prioritise higher resolutions and/or graphics settings.
i think what mangocat is talking about is the capacity of ram. 16gb will still do mostly fine nowadays, but if ur looking at ddr5, 16gb kits dont cost much cheaper than 32gb kits, so 32gb is a better pick and
should last u longer, especially since games are always going to become more resource intensive. ram speed matters if ur getting non x3d ryzen, though just stick to 6000mhz cl30 if u dont want to tune ur system beyond setting memory profile.
most am5 motherboards available locally will get the job done. something cheap like the msi b650m gaming
plus (avoid the non plus) will be good enough for most people.
when u have a dedicated gpu, u dont use the motherboard outputs.