$4500 is the key resistance level, that's where I'd personally be considering selling my bitcoin and looking to buy the dip, if the price broke through to about $4700 I'd look to cut my losses. Even if we do break the $4500 resistance I don't expect it to be at the first time of asking.
My opinion is that you can sell partially, and leave rest position for the resistance break level scenario
This is always wise, you don't want to risk your full amount in one trade, unless you have a high risk appetite or you're only sitting on a small amount of BTC. In this market I'd never risk my whole stack on one thing happening because it's too unpredictable.