I have answered this question before and, for now at least, I am holding off from releasing my portfolio to the public. In general, the less exposure you have to investing, the more you should have in Bitcoin. For most people, cryptocurrencies are a first time experience with investing and you will both lose and gain substantial amounts in short periods of time. Bitcoin has lower % swings than other cryptocurrencies so can be easier to sleep at night and it's the most important one to understand. After that, you begin touching other mega caps as you mentioned.
I don't think that it is all that important that you are well diversified into a ton of altcoins so much as it is that you have some allocation in Bitcoin and some allocation in altcoins so that your portfolio enjoys some benefits associated with less than perfect correlation.