Coinbase and Gemini are user friendly and U.S. based. Gemini is owned by the Winklevoss twins.
If you want to invest in "alt coins" the smallers coins, use Binance and/or Bittrex. Binance is the biggest one though.
Invest what you can afford to lose because it is a very volatile market.
Don't ever leave your money in the exchanges. It is still the "wild west" and exchanges can be hacked and you can lose your money.
Get a cold hardware wallet like a Ledger Nano S so it won't happen to you.
Twitter, Reddit and YouTube is great for news and community. You can also visit coindesk.com or cointelegraph.com for headline news.
For me, the end game is to accumulate as much bitcoin as I can before global mass adoption. Bitcoin is king of all crypto. You buy other coins with bitcoin then sell it back to bitcoin. You can do the same with Ethereum and Litecoin.
As of right now, bitcoin is around 85%-90% from the all time high so yes it is a good time to buy.
Current price is $3366
All time high was $20,000
You can always do "dollar cost averaging" strategy if you're in it for the long haul and technology.
Learn it. Have a game plan. Have an exit strategy.
And I have to say this... THIS IS NOT FINANCIAL ADVICE.