The best advice I can offer you is not to feed mice to tarantulas. Since they're inverts, tarantulas have no need for the calcium that is found in rodents and consuming it can cause them health problems such as a wet (difficult) molt that they might die in. I know in the wild they can resort to eating mice if necessary, but as a pet owner, if you want your tarantula to live a long life, it's best to feed insects such as crickets, meal (super) worms, silk worms, etc. Enjoy your tarantula, the Grammostola pulchripes (Chaco golden knee) is an excellent choice for your first one!