I will add my humble and less than experienced opinion. Less than because I do not have a system that compares with yours. Having said that, if I was looking at spending $30k for a phono preamp, not to mention the cost for the rest of your system, I would be looking in the $40k-75k arena of turntable, arm, & cartridge combinations...at least. So, this is what this pauper would do:
1. Follow @terry9 advice. Get on a plane or three and invest in listening sessions. You’re going to spend 10’s of thousands of 💵, do this foundational work.
2. Be patient
3. Do more research on other turntables, tonearms, and cartridges.
4. Reach out to Jeff Dorgay with Tone Publications. He’s very knowledgeable and has extra systems as spendy as yours. He’s also not a pompous #@&! like a certain self-proclaimed analog expert who won’t review certain tables because he doesn’t like the design, engineering or the fact the mfr doesn’t bow to his excellency. Sorry, back to the point. Jeff’s a great guy.
5. Check out Basis Audio. The late A.J. Conti dedicated his life to turntable and tonearm engineering. They have standard bearing and air based turntable systems. You can hear for yourself which you prefer. Their bearings do not go bad...period.
6. Choose two different cartridges, one being Koetsu and the other ____?_____. Everyone should have a Koetsu If they can afford it. If you get two tonearms, you’ll never regret having two setups. Regarding a mono setup, I ask myself, "how often will I play a mono album?" If it’s 1:100 or more, I’d rather spend the extra 💵 on better vinyl or something else. That’s me.
7. @millercarbon has good advice regarding the cost to performance ratio of a table/tonearm compared to cartridge. That said, I think you’re investing enough in the rig that short changing your cartridge selection would be criminal or near to it. No disrespect to mc, but a $15k cartridge should not only not be overlooked but rather expected given what you are likely to spend on the tt/arm combo.
8. Be patient
Goodluck. Please share your experiences listening to different rigs, dealer encounters, and final decision. Thank you for the invite into your journey.