1-It seems US downgrade to 4.2 and EUR downgrade to 4.5.
2.Yes. You need to install for first time. After that you dont need blue card to use ds profile exploit.
3-Afaik emunand is seperated from your sysnand. You dont need to create another emunand.
4-Yes.Big card from 3ds itself.
My friends don't even know what 3ds is. Maybe i can buy used one from gamestop or somewhere online. I am waiting for update to buy 3ds. If there isn't gonna be emuNAND i will be looking for 8.1-9-2.
I may try the new ram site, and download more RAM to my Switch. Not sure if ddr3 is the right ram
for it tho. Edit- no it uses floppy Ram, just like @AncientBoi