all coins in top 100-200 are good to invest. Just choose 5 and invest
I don't think so. Some coins currently in the top 200 got there in a flash due to pure pump speculation, and they won't survive 2018 because they don't have a real community behind them, only a bunch of greedy day traders.
One has to study a bit, check out the coins's history, the dev team, the purpose.