What's a good way to practice ledge sweet spotting? I'm very bad with spacie recovery.
There are plenty of different ways of getting the sweet-spot. With side-B, get used to angling the control stick up or down in order to sweet-spot on the fly and to trick the opponent into thinking that you will side-B on stage. Alternatively if you can consistently shorten the side-B, use the shorten to juke the opponent and sweet-spot when they would read the stage recovery.
With up-B you can aim downwards towards the ledge from above, and while in the up-B animation rest the analog stick in the neutral position to automatically grab the ledge from any distance. You can also use double jump to put yourself perpendicular with the ledge to easily up-B sweet-spot, this leaves the option to recover on stage if you see them about to grab ledge. Another trick to learn is the many up-B angles. When close to the stage wall you can almost always sweet-spot using the slightly tilted upward angle towards the stage.
Those are really just tricks though, to learn how to sweet-spot confidently is just about dedicated practice to learn the exact distance. Try going to FD, dropping straight down from ledge and up-B'ing, continuously until you get the distance down, then do it from the 45-degree angle.
On the subject of recovering, I currently don't use shine-stalling at all, and I am not sure where it is useful. Does anyone have any tips on this?