We pitched your suggestions at our developers for you.
They've responded that whilst the Samsung Notes app already has some limited capability with Android supporting features such as spell checker, there are no current plans to extend that.
Regarding Night Mode for the app, they've said that the black background in that mode would make any notes/drawings made in black in the app invisible, and so have decided against implementing the suggestion.
Always happy to hear ideas and suggestions from you guys - so if you do have any more, definitely let us know.
Say "Hello!" to the Community in The Introduce Yourself Thread.