Just try it with the old laptop. I personally found dietpi the incredibly easy entry. Super bare bones Linux actually meant for raspberry pi and such, but you can run it on any old laptop. Using your all gaming rig might be a high energy usage if you're just gonna run barely more than a NAS. If you do it with the laptop, take out the battery or put a timer on charger outlet, permanently connected and charging with a system that isn't actively managing the battery and charging could get you a spicy pillow quickly.