55-59 spine should do you well. Diameter for most woods will be 11/32, altho you can get that spine and your 500 grains in 5/16 with ramin. Ramin is a good arrow wood and tougher than most. Fir, cedar, spruce or the hexpine can all be had with your specs. Yes, the hexpine are very good shafts.
For target arrows, you could easily drop down in arrow weight to about 9-10 gr/lb (400-450 gr) for a little quicker flight and flatter trajectory. Fir or Sitka Spruce would be my choice there.