That's the point of Duolingo - if you were only learning useful phrases (where is the bathroom, my name is x, etc.) there's a chance you'd learn those phrases off by heart and not actually learn the rules of the language, whereas having to translate random sentences like this forces you to actually think about grammar and stuff! If you want to just learn phrases that you will definitely use, a phrasebook for tourists is much more helpful than Duolingo is. :)
So you don't need the "ja" in a sentence like this? Is it like Spanish where you can omit the pronoun?
Yes, dzięki is also accepted here. Generally, thank you = dziękuję and thanks is dzięki.
Well, technically it can, but that's rather rare to say that, I don't remember anyone ever asking for such an option...
In the sense that dziękujemy means we thank you - yes. But you tend not to use the pronoun in English.
Well, the sound is ę (eu, like Spanish for 'Europa' or 'euro'), which can in a way sound a bit like 'en'.