What size tank? People used to recommend 2 pounds per gallon, but thru lots of trial and error that amount has been reduced to about a pound a gallon. It also depends on the density of the rock. the lighter and more porous the rock are, the less you need. Are you buying fully cured or uncured rock?
I bought a little over 1 lb/gallon of live rock and later added a bit more, but as my octo grew, I found I had too much live rock. I've had to reduce the amount back to 1 lb/gallon.
As for sand, figure about 1 inch of fine sand - use aragonite sand to help control your pH. Wash it thoroughly (this may take some time and effort) before adding it to the tank.
Nice of your dad to chip in some cash for your octopus project!
Be sure to allow enough time for your tank to cycle - we suggest 3 months.
Also, as Colin once suggested, you need to figure out a source of shrimp and crabs before your octo arrives. It would be good to have lots of amphipods living in your tank for your octo to eat when he arrives, too.