To play off what others are saying i think a mini pc and a stand alone nas may be the better route for you. It may seem counter intuitive to break it out into two devices but doing so will allow room for growth. If you buy a creeper bare bones mini pc and put more of your budget towards a nas and storage you could expand the mini pc without messing with your nas. You could keep the pi in the mix for a backup if your main pc is down or offload some services to it to balance performance.