Normally you just sparge up to your boil volume. In batch sparging, you measure your first runnings and sparge with the amount you need to hit your boil volume. For fly sparging, some simply math will help (but again, stop at your boil volume).
For temperature, I use Beersmith because it does the calculations for me. But there are other free calculators on the internet, or you could do the math yourself if you're so inclined!