High and welcome to the community.
1) If you go to Tools/Options/Region priorities you can set your preferred region there and this will effect imports also.
2) If you need to change the emulator for a full system you can use the bulk edit wizard. Just click on a game then ctrl a to highlight them all then right click a game and choose edit, this will open the bulk edit wizard, just choose emulator in the first dropdown then your emulator in the second.
3) The anolog triggers do not work in Bigbox unfortunately.