For the corner you need to use a two-part wood putty that will provide better structural strength. A lot of people use automotive Bondo, but I prefer a product that is designed to match the expansion/contraction of wood. Bondo makes a filler intended for wood, as does Minwax (High Performance Wood Filler). If you want a true epoxy, which gives a longer working time (and is elastomeric) I would go with Abatron WoodEpox or J-B WELD Wood Restore Premium Epoxy Putty.

While most will say semi-gloss, the answer is it depends. See the following post for more info.

https://pinside.com/pinball/forum/topic/best-touch-up-paint-to-match-black-cabinet-and-black-sides-in-pins