Should have good knowledge for both investing and trading. But trading requires more intelligence and knowledge than investing. Investing should be done for a long time, if you invest for a long time, you can expect more profit. Chances of loss on investment are less. But should not invest in altcoins, it is better to invest in bitcoins. Trading is done for a limited period of time. Traders buy when the market is down and sell when there is some profit. Investing is also risky but trading is slightly more risky. I have invested in Bitcoin. I prefer investing to trading.
Indeed. Both trading and investing require sufficient knowledge. It is impossible to invest or to trader properly if we have no sufficient knowledge. That's why we never begin trading or investing if we still have lack of knowledge. We often saw many suggestions in this forum that the beginners must focus on learning first before they buy-sell crypto on the market. It is absolutely true, knowledge is the basic thing to have both for investment or trading.
Regarding how long we invest in a coin, it depends on our goal. Each person has his own goal, there is a person who wants to earn fast profits ad there is a person who wants to hold coins for long term profits. However, the point is how to choose the right coins for our investments. Surely Bitcoin is the most recommended coin, but I think it is okay tp invest in altcoins as well. As long as the altcoins have strong fundamentals and have no bad issues, the altcoins deserve to choose for our investments. Commonly, people prefer to invest in the top altcoins that have the strongest fundamentals.