Can I install 2 RAM sticks of different types, like 16+32 or even totally different manufacturers?
It should work but never best practice.
Sure but they will run worse for it. At mismatched speeds they will run at the slowest speed that both support. Expect extended memory training on first boot
you will also lose dual channel support because that requires matched pairs.
Not necessarily, if you watch the video linked above, you will see that if asynchronous dual-channel is supported by the processor then matched sets of ram are not required with some limitations
No idea if Tiger Lake supports that feature however
In most cases you don’t even see the differences