Notes

If you always open an existing note, with at least one character formatted the way you like, the modify and save your Note, you could get what you asked for.

You may be able to create that starter 'stationery' and locking the starter stationery you want to start with each time. Then when you change it and save, the starter would not be destroyed.

Sure...

Yeah, Notes, just like any Apple app uses the system default fonts…and no it can’t be changed… only after you type something and select it and change the font manually…