in coinmarketcap you can see the top 100 exchanger and the many of traders and volume maybe you can add cash also but idont if that is recommended...
Don't stop at the top 100 but be able to see any altcoin if it's listed on the coinmarket
but i think we can only choose the top 100 if we are new person because we need to understand the basic learning about trading and its only learn by doing in trading and keep practice. i think the top 50 is enough for us to still continue learning trading because there is many people will interesting too with bitcoin and no one can share their method to reach the profit. if you can do with 50 coins then i am sure that you can watching the price is up and down so you can make your own decision to buy at what price.