Need help with my new Guinea Pig?

I just got my guinea pig today from a lady from Craigslist. She has had them for over a year and she said that he is very loving. That he would purr when they would walk buy and very cuddly. But, I know that he is under stress from switching home environments. I am trying to have him get used to me and he is letting me pet him and will eat treats out of my hand. But, still very scared. I am wondering how long it may take for him to trust me enough to pick him up. He came with a cage and supplies when I got him. I also got a way bigger cage that has levels and toys that will make a guinea pig more happy when I am not around. What should I do because I am too afraid to pick him up yet. Should I just keep him in his main cage til he gets used to me? Anyways, if you have any information that can help me, that will be very nice. Additional information is awesome too! Thanks [=