I'm trying to build a console and end table. For the console, I want it to have a thick reverse bevel look on the inside, so I will be cutting a long 45 degree bevel in the bottom of each piece of 1x4x72" and 1x4x32.5" and then butting/joining them at the corners. I cannot figure out the angle at which I need to cut the corners in order to have them sit against each other without any gaps. For the end table, similar issue. I have to join 3 pieces of wood with long bevels on the bottoms to form the base. I also need help with those angles.

Hey there. This is my first project concerning wood, and even then, I'm remodeling a bookcase. My problem is I used an angle grinder ( was desperate cuz nothing else was working) and it worked stripping the paint off but I have these gradual bumps all over the wood. As a beginner, sanding seems like the right thing to do. Though, I know if I go about it wrong, there is no going back. Like don't know what kind of sander. I heard a belt sander is a little more aggressive which might be useful in this situation but not certain. I am afraid I already messed it up enough as it is.