1. Where do you trade altcoins/bitcoin and why? Bittrex/Poloniex?
2. Where's the best place to change bitcoin/altcoins into FIAT with the lowest fees?
3. What's your strategy in trading and how much do you invest in it?
Thank you so much for all your answers!
I swing trade BTC on GDAX and I hedge for the short term on Bitmex. I consider GDAX the best place to sell for fiat (but they only offer fiat markets for BTC, LTC and ETH if you are looking for other altcoins). By using limit orders, you can pay zero fees on GDAX.
I started trading back in 2012 and worked my way up from a < $200 deposit. I don't use much margin and I focus on catching the bulk of moves on the daily/weekly charts. I've also learned the hard way: if you are holding either BTC or USD (BTC for weeks or longer, USD for months or longer), get it off the exchanges. You never know when an exchange might disappear with your money, get hacked, etc.