thank you for the update, hope you'll find new members soon <З
and about ml, I'm totally team Emperor, the age gap is not that big, only around 5 years, and our heroine mentally is a full adult actually, so ideally they just should wait for a few years to become a couple (maybe use a time skip)
for me, personally, any other male character is ok as a ml, but god forbid for Grand Duke to become one, I just despise his character archetype, aka little spoiled tsundere brat, plus, as I mentioned, Nina now has the mind of a grown-up, but Duke is soo immature so it would be really strange to see her reciprocate his feelings