BTC most of the time determines the prices of other altcoins though there is some slight resistance i really dont think is that much so i will advice you watch the market closely and get out as soon as you take much better profit
Not always. In 2019 Bitcoin almost doubled in price, while most of alts stayed the same or even lost value. It will for sure not be same in 2020. Every coin have some own flows. Yes some are more connected to Bitcoin some are way off. Coins without any use case will slowly go towards zero no matter what.