For example, if you google Coinbase, you will find plenty of people insisting it's a scam?

It seems like everyone calls everything a scam in crypto lately.

To be fair there have been a lot of scams, but if you do some re-search and read around a bit more you start to realize the difference between real block-chain startups and scams.

Coinbase has been a legit exchange for many years, I would recommend using it. Others I would recommend are Kraken, Gemini and Poloniex, the last one is crypto to crypto only. (if you don't count in Tether)

As a safe wallet I would use blockchain.info and for Steem your own personal Steemit account and make sure the password is safe and hidden. :)

Welcome and good luck with trading! I'd recommend checking out @ozchartart's blogs for indicators or interesting currencies who might or might not be on the move. :)