All those things should work OK. For iMessage all I had to do was to follow the guide and use iMessageDebug to make sure all the iMessage-related stuff stayed the same from reboot to reboot. For audio, if you just use the 100/200/300 series audio support patch and the ALC1220 options in MultiBeast and, then, under audio in Clover Configurator, tick ResetHDA and inject layout 11, you should be OK.
For sleep I don't know - mine always just worked. I am injecting iMac 18,1 instead of iMac 18,3 because with Radeon graphics (RX560) the 18,3 smbios caused the display to lock up from time to time. I have the internal Intel graphics disabled in the BIOS.