A standard resolution to work at is 1920 x 1080 (HD , 16:9/1.77:1 aspect ratio).
One of the advantages of programs like Harmony or Flash (Animate) is that you can draw or make notes outside of the main drawing stage or camera view. You can do that with TVPaint, too, but you have to set it up properly when you start a New Project.
When you go to File Menu > New Project (Shift N) , in the New Project window there is the option to set the Project With Camera View. This creates a scaled up project size with the Camera View set to the desired output resolution (such as 1920 x 1080). You add 120% , 150% , 200% , or whatever you want. I usually scale mine at a ratio of 200%. This makes the overall project size 3840 x 2160 , with a 1920 x 1080 camera view.
All the animation is drawn to work within the 1920 x 1080 camera view window . Anything outside of the 1920 x 1080 camera view will not be seen when the project is exported. The excess area around the Camera View can be used for Notes.
Another reason to create a project with Camera view is to be able to draw the character out further beyond the edge of the screen (off-camera), such as when a character is walking on or off and their legs are not necessarily in view , but it's helpful to the animator to be able to draw out the character's feet and legs beyond the edge of the frame to make sure the placement is accurate as the character enters or exits.
When you're working on the animation at full size , you can size the window so you're not seeing the margin areas with the notes , but whenever you need to check the notes or add notes , it's easy to pull back to see he margins around the Camera field.
If you were to create a Project With Camera View that is sized up at 120% you'll have less margin area to work with for adding Notes, etc. , but it can be enough. I find that usually a ratio of 160% - 200% is more comfortable for me.
(again, when you export the animation to .MOV or .MP4 only the animation that is drawn within the 1920 x1080 camera field will be visible.)