Is Gemini platform for trading reliable ?

Yes, I like it. Coinbase is a money guzzler, avoid it of you're buying crypto.

Yes

Really reliable, and low fees compared to coinbase. For EU folks I would advice Kraken since you can do SEPA transfers, but its engine is not as reliable

Great platform and low fees (and low prices!) but simply not enough coin choices. Needs some altcoins to be fun.