great question about atzmus
from what i understand your whole problem is on the atzmus part – meaning if the atzmus part makes sense everything else in your questions pretty much makes sense and just needs to be fined tuned.
(as it looks like the moshiach part you can handle especially based on sanhedrin 98B based on poshut pshat and the meforshim there E.G. chasam sofer, pri tzadik, sdei chemed, beis shmuel in shulchan aruch regarding “ksivas get” and others)
there are a few options either we can try explaining it to you or you can ask a lubavitcher you respect (YY Jacobson was mentioned)