You should get it a membership fairly soon when the attack and strength are around 40. It would give you access to better spots that are less crowded, and if you like to bot you could start botting your character with probably less of a risk than you would have botting on f2p. As soon as you feel you are high enough to do some quests, start questing your defence up until you reach 45. There is a fantastic guide here on Sythe that will help you get all the way to 45 defence without having to train a single level
Guide to a perfectly quested zerker:
http://www.sythe.org/showthread.php?t=1172388