You must calculate your capital on that coin first, for example now the price has given you profit 30 % from your capital, i think that is good time to sell your coins. If you want more profit, you may wait for few days again. But, remember that the price can be bubbled anytime, try to satisfy with less of profit and not to be greedy.
Yes. If I personally buy when the price goes back down and sells when the price goes back but even if the price goes up again for example I will not sell everything but I sell it as needed to rest, I hold more while waiting for the others. Price increases at relatively large prices