4. To be honest, the best coins to invest are the top coins or have been listed in the top 10 at CMC.
When you are investing in top coins you don't need to check a lot of things, others did that for you. What people should do is to prepare some money and buy coins they believe in long run, after that is simply waiting. Crypto is good for making money in long run, and its the safest way from them all. Everything fast can be very risky, and usually chasing for quick profit leads to losing invested money.
That is the key to all of this, investing in the top coins in the market can be one of the best decisions that you take in your life but it is important to understand the nature of that decision, most people want to obtain profits in a really fast way and if you invest in those coins you should not really expect for that to happen, it will probably take you years to see the profits that you want but when you finally get them you will not be disappointed by the results.