Painting the buffet off white will make it feel lighter to the side of the room, and the black table and chairs will anchor the center. To tie them together, consider an off white upholstery on the seats, and a table runner on the black table, with a centerpiece of some sort - a bowl whose contents can be varied by season, a grouping of candlesticks, something to contrast on the off white table runner. We see contrast before color. (Judyg's suggestion of white chairs can work too)
You need art on some of the walls - even framed posters for now will warm up the space and give you a touch of color. Look for vintage posters or something from a local museum which appeals to you. Much better and longer lasting than a trending accessories from a craft type store.
Over time, you can purchase a painting found on a wonderful vacation, or add a piece of architectural salvage. If you want to bring in a mirror, be sure to check and see what it reflects before you hang it. You don't want to bring dirty dishes in the kitchen sink into the dining room because of a mirror, or have a great view of the powder room door.
Good luck, have fun, and don't be afraid to experiment. Try to set a budget for home improvements, and save a bit each month, so that when you do know what special pieces you want to add, you have some savings for it.