You can buy bitcoins in bits(0.00002BTC, etc). You don't actually have to buy one whole bitcoin.
What altcoin should you invest in? Go to
https://coinmarketcap.com/ and do research on those coins, then YOU decide which ones are worth investing in.
This guy sums it all up.
It's worth doing your own research and finding a coin that's solid. If you're after a longer-term investment, look at the solid projects that have history, a roadmap, and lots of support. Hedging your bets on ICOs can be dodgy, trust me I know. I invested in Electroneum...didn't turn out too well; bye investment.
Good luck out there.
-Knightly