I'm willing to invest into crytocurrencies but not sure how to start ones I'm ready to dive in. Shall I go through Bittrex, Coinbase or find a legit seller here in BTCtalk? What would be your advise?
I don't think finding a trader here is not a good idea because you are newbie so there are chances for you to getting scammed,so go with the exchanges.
There are lots of exchanges are available so choose the exchange based on what coin you are buying,if you are buying only the bitcoins then you can buy with coinbase exchange and it is one of the simple way and also you can buy the bitcoins at the best price in coinbase.Or else you can buy with localbitcoins.com and it is almost available in all the countries so you can use you local currency to buy bitcoins.
Or if you are looking for other coins then poloniex exchange is a good option and most of the other exchanges closed the new registrations.