I understand you are getting the Rosewood Signature Platinum (outstanding choice in my opinion). Koetsu cartridges are somewhat unique in terms of having a rich, warm sound without being murky. If you own just one cartridge, that is a great choice. I understand you have multiple arm wands, so you will have other choices.
Interestingly, I know a few Garrard and Thorens idler fans who own Rosewood Signature Platinum cartridges who like the Audio Technica ART 1000 cartridge. It is a different sound, not quite as warm, but it is very good. I would add that to your candidate list.
It seems like you will be having a lot of fun messing with different setups, accessories, etc.