I am ripping my CDs using a multi encoder. ALAC is used for Itunes and FLAC is used for Winamp.

Im guessing that means I have to tick all the boxes in the Replay Gain Settings? Example:
tick - Write Track Gain
tick - Write Album Gain: album identified by - Album ID Tag
tick - Write ItunNorm tag for Itunes (if album gain is enabled this is written)
tick - EBU R128 Calculated Gain
-23 LUFS Target Volume

Is the Itunes tag a seperate tag? Or is there only one tag? In which case I need to decide whether its written for Itunes or Windows based products?

Is there any disadvantage of ticking the new form EBU R128?

Do I need to think about the -23 LUFS Target Volume or just leave it as default?

I have not started applying any gain control with compatible player yet but I want to make sure I get these tags right first time if possible.