Start learning songs right away if you can get good tone out of all the involved chords IMO. It makes the practice sessions much more fun IMO and you will be practicing chord changes at the same time. Thats how I did it. It can be a little frustrating to play your favs slow at first but don't worry about it. Speed and accuracy of chord changes will comes soon. I remember thinking "lll never be able to play this song at the correct tempo" but now, a month later, I'm playing it at tempo without even looking at the guitar. Just pick a song you love and spend time practicing it every day. It really helps, especially when it starts to become recognizeable to you. Very encouraging!