How do you select promising coins?
How many coins should be in an investment portfolio?
How do I buy, all at once or in part over the course of a month?
How to deversify risks and rebalance ?
Starting with 5 coins for your portfolio is a good idea. I am strong believer in diversification. So for my portfolio I have around 60% in bitcoins and the rest is spread out across multiple alt coins. In the beginning I had some money to invest so I bought all the coins at once. In my opinion it's best to just hold for a longer period of time if you don't have the time to constantly be up to date.