Just adding a few thoughts:
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If you already use Omada for APs it might be worth it to use their switches as well. Makes networking fairly easy. MKs are nice (I use them together with Omada myself),but basically everything you would need can be achieved with the Omada Switches as well. Only for the actual Gateway/Firewall I would rather go with OPNsense or, in a pinch, MK, with the later being inferior to OPNsense.
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Multiroom Audio I would very much recommend Amplipi, but I also might add that central audio with reasonably high quality is not as easy as it sounds electrically - I have seen more than a few installations that failed due to induction from other sources, timing issues,etc. It is sadly harder than one would think. It gets much much much harder for TV/motion picture relevant things as things are even more timing sensitive then.
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have a look at KNX for all smart home related things. It's the gold standard.