As long as you have more than 10, it's fine - although the more you have, the less times you will have to go back to re-equipping arrows each time (and wasting xp)
As for the GP, I can't remember how much is used, but it's not a lot of GP, 100k will probably last you an entire 8 hours of botting. (?)
Best items to buy = the best ranged bonus you can wear, so you can score higher points and gain more xp