In general, the sticks should be from the same batch - more precisely, consecutive serial numbers. And as the other comments say, AM5 and 4 sticks is a gamble - especially if you want to run them with 6000MTs. You can try, but if it absolutely has to be 4 sticks, then I'd buy a matching kit.

That depends on your bios and motherboard. In any case, I have been running 4x32gb for a long time without any problems. But I don't overclock to the limit either, which isn't intelligent anyway.

I had 4x16GB in it and it went max. 3400 MHz, then switched to 2x32GB, 6000 MHz without problems.
Depending on the motherboard, the cables for the 2 additional sockets are simply a bit longer and certain timings/frequencies are no longer stable, regardless of the voltage.
Buildzoid on Youtube has some tips on these bars, with timings etc., but it didn't help me because of the mainboard.

As Floowy says, it's difficult to say. With DDR5, it is often said that the system is less stable when fully loaded. To be honest, I would just try it out; otherwise you can send two back if there are any problems.

Mfg

It is difficult to say without knowing what kind of mainboard and what bios version is present.