Enclosure will protect printer from dust and it will also keep the ambient temperature more stable. Dont make it hermetic sealed, better add few holes on the front and few on the back for example. I have a low rpm fan with dust filter because I mostly print PLA and in long prints (12h+) temperature can go a bit too high if there is no airflow at all. Keep in mind that enclosure should be removed sometimes for mintainance, removable sides is what you should look for.

You can leave filament on the printer, but if you dont use it for a long time it could get wet and then you have to dry it. Keep the rest of the spools in plastic sealed box or bag and put some silica gel inside.

Full calibration should be done once, but fine tuning when you face some issues or when you change to different brand or filament type. It depends how well the printer is assembled and how experienced you are, it can take only 5 min every few months, but begginers can spend days sometimes.

Extra tips: clean your rails and wheels whenever you can (once a month at least) for dusty garage. Get a kitchen sponge, drill a hole in it and guide filament trough the hole to remove any dust before extruder.

Welcome to the most fun hoby and happy printing!