Alacritty (Kitty is also good)
Nautilus or maybe Ranger (or just doing file stuff in the terminal)
whatever the default is, and I use rofi for launching programs
Keep Budgie/Mate Stuff or remove it
leave it - it's nice to have options, and having it installed isn't hurting anything
If you remove the Budgie/Mate Stuff, are you using GUI-Tools for system-management? (e.g. lxappearance)
yeah, I use lxappearance for GTK theme selection and stuff!