Up to you whether to hodl or not because that is investing and you gotta decide whether you want to be in BTC (grow less but more stable) or go more aggressive but risk the chance of ruining yourself. As to the 20k BTC in 2018 I don't see why not it couldn't happen. It is barely over a 100% increase and that to me seems easily feasible given how many hard forks and how much institutional money is coming to flow in soon.