If it’s recommended I would oil where the manual suggests just don’t put too much in, hoping you won’t have to next month.  They wouldn’t suggest it if it wasn’t necessary. 

your machine may sound noisy because it needs a new needle, it should be changed every 8 hours of stitching.  If the needle is punching through layers it will blunt, and if you are using water soluble stabiliser it blunts quicker.  

if your bobbins are the plastic type, yes I would reuse them, especially if they are Janome pre wounds.  If they are generic then I’d wouldn’t be so inclined, but that’s my personal opinion I don’t like generic bobbins, I only use Janome, they don’t clatter and bounce in the machine.

if you’re having problems with threading, check your manual to see if you can move the hoop, there’s normally an icon on the machine to move the hoop so you can trim threads or adjust between colour changes etc