Some rigs you can run the generator while plugged in - others you shouldn't - so to be safe, unplug first and it's always safe on all rigs if unplugged. As to the battery disconnect, I've never used mine - never had to - well once, when I had forgotten to unplug an electric heater when I unplugged from electric and that caused a drain. But until you know if you have anything pulling a drain, it's not a bad idea to do. Again, some rigs it's more important than others. As time passes, you'll learn your own rig - and what you have to do, what you probably should do - and what doesn't matter so much for you.
RV air conditioners work much on the principle of room/window ones - and have filters you need to clean. Well, in a house, you need to replace the filters in furnace/air conditioners - in these you just have to clean them. Don't forget our maintenance room - where this whole thread probably should be - but this is mentioned in a thread I wrote sometime back that lists lots of things we need to do.
And I agree with Tina - I have learned much more by making my own mistakes Actually by doing it myself. You learn by doing - much faster than by watching!