i think two are enough, if you are low on sp
, the skills i use for grinding were always imbue+ antidevil + arrow combo because thats all i need to kill a white-green mob (im lvl 77)
stuff like mind bow, devil arrow (berserk/demon) and strongbow are nice too, but only if you have the extra sp.
arrow combo+antidevil arent really as sexy as stongbow or devil arrow

but they do as much as strongbow on a crit and, does it faster and also has a shorter recharging time.