Hi. I removed some awful "baseboard" (a piece of wood with a quarter round nailed over it at the floor) and found an even bigger mess in two places.

My goal is to paint the wall and trim in this hall all the same colour to try to hide the door mouldings (this little hallway is basically just a collection of doors leading elsewhere and the whole thing looks very cluttered)

Now I have this gap in the floor, which explains the quarter round coverup. I have little skill and limited tools. Can someone offer some advice of how to tidy this up? The walls are not square. Wartime home, plaster walls. At this point, I wonder if I should just smooth things out with spackle and paint, but the floor is obviously going to look terrible. Any thoughts on this are much appreciated!