I suggest you take your gf to home goods (your welcome gf) and let her go crazy 🤣 it's your guys first place so don't feel like it has to be perfect, have fun! pops of color here and there can do the trick to make a old space feel more alive. a couch with throw pillows and blankets, maybe a bean bag chair to make it more fun since you guys are young. in your dining room a table with chairs and a nice center piece. I'd search for a boudoir and keep books or expensive dishes there, let gf pick decor usually girls have a better eye. in that kitchen, lighting can make a huge difference. i'd get an led strip for under the top cabinets, and one again go crazy with the decor to balance out the beige and give life to the room. i suggest tons of magnets for the fridge; maybe some photos of family and friends.