I don't know how far you've gotten so I'll start with this link on exchanges:
https://steemit.com/cryptocurrency/@mikeflow/beginners-guide-to-cryptocurrencies-how-and-where-to-start-buying-and-trading
This one on security:
https://steemit.com/cryptocurrency/@mikeflow/warning-all-cryptocurrency-holders-please-please-take-action-now
You should have some exposure to the big 3 coins you mentioned. I try to buy more on big dips in these.
Other coins with great potential are:
NEO, OMG, QTUM, BNT, CVC and STEEM.
Good Luck!