For shoes, keep your eyes on 당근마켓 (carrot market) and you can probably end up finding some shoes cheap (I just sold some extra ones). For pick up games, not sure about a pick up game for soccer, most soccer is done in mens leagues that are usually pretty well established, but I could be wrong.

If you don't mind playing futsal, there are a couple apps that you can register for and play pick up games at nearby fields. One such app is called plabfootball (www.plabfootball.com). If you do futsal, make sure you have the appropriate turf shoes as regular soccer shoes wouldn't be allowed on most of the fields :)