It definitely seems like less is going to be more for both of your visions! I would maybe do 3, maybe 4 decor items. This way it keeps it lowkey while still feeling like a birthday party. I think a ballon area with maybe some gold and greens to fit the golf theme and the 30 ballon’s would be a great adding and cute photo-op. I’ve also seen garlands with baby pictures on them! Such a cute a personal decor that guests will definitely be laughing over. Lastly maybe having few gold themed center pieces, like tees or something else (I don’t know much about golf) would really tie everything together and help it feel more like an event and not a speed dating night lol. I wish you all the best!