On a 17k gallon pool, you would ideally have a flow rate of 36 GPM (8 hour turn-over). That translates into a 21" ID sand filter @ 15 GPM. You'd want a 18 sft DE filter or a 96sft cartridge filter. Cartridge filters can be oversized without limit; DE and sand filters cannot.

The 'real' flow rates for filters are the ones listed for public pools:

sand => 15 gpm/sft
DE => 2 gpm/sft
cart => 0.375 gpm/sft

The Superflo pump may, or may not, be too big. Two questions:
1. What is the exact model of the pump, and what are the electrical ratings on the motor?
2. Are you handy enough to take the pump apart, and re-assemble it?