2 is not entirely wrong tough. Sometime i trigger route automatically if either conquest or reign is higher by one point so i always try balance them both. I guess between 20 and 24 you can still can have them safe in not equal number but if past 25 it always check which one is higher (Mostly i got 27/27 or even 29/29 for each playthrough)
For 3 you can always mingle up to 98 in the very beginning but doing that will give less trigger call event scene so it adviceable for doing mingle first up to 40 0r 50 point then doing train reducing goddess divinity to 20-30% while stop mingling. After you can continue doing mingle the goddess again
2. That is again incorrect - the only way you can be automatically locked into route is if you have over 30 conquest OR under 20 of both reign and conquest. At least I have not found any other combination that leads to being stuck in the route.
I had as much as 6 point gap and it never lead to being forced into a route as long as both reign and conquest were >=20 and <30
As for 3 - you don't miss those events actually, you will get them once you corrupt the goddess and skip a turn(need to skip 1 turn per each event).
So mingle 98 is a very good idea if you only plan 1 playthrough, since it will save a bit time on 'unique save'.. and overall a good idea as well if you plan to save scum your way for more scenes.
As you can see - many wrong rumors spread everywhere and that's exactly why I am making my own ending/easily missable scenes guide, which will hopefully be 100% correct and will solve the problems with partially incorrect information spreading everywhere.
Actually the ending/extra scenes part of the guide are mostly finished, you can check it right here(link below), if anyone who is 100% sure(not just 'you think') about something being wrong(which will highly likely be some typo at most, since most of those are already 100% tested in conditions I mentioned) - you are free to correct me.
Same if you find something that you wouldn't otherwise be guaranteed to get in the process of unlocking all endings(like the good/bad and bad/bad combos of girls that I mentioned there)
The only endings I have yet to get is the 8 fena and 9 fena one to confirm them and maybe add some more info regarding them.
Also not 100% sure if all extra endings are available in conquer route or not, I was simply thinking it's not worth the effort to test it as some are just outright easier to get during reign, but either way, here you go:
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EDIT: Just found out that garm actually gets upgraded(seemingly via conqueror route) and is pretty good at that, getting 20 poison blast and 2 additional attacks, becoming a rather good unit.