For size of a mac mini, you can go for NUD, but those may not give you the best performance. You can consider i5 6500 + gigabyte h170n wifi + 4gb * 2 ddr4 (i believe cheapest are kingston value ram, but not sure) + antec vpf350 + sp920 256 ssd. For case, you can consider cm 110 elite or silverstone sg13? I am on my phone so I can't type out a full list / price for you. Maybe you can check on jumbx/centralfielx yourself.