Tried searching for a bit and couldn't really find an answer - how does compatibility with parts work?

I have an i7 -3770 and a lga 1155 motherboard. I have a 1070ti gpu as well.

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I checked a website early but it only had a small handful of certified cpu's on it and in general I was a bit confused.

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How much does compatibility matter? Is it worth giving this whole thing a shot with my current hardware?

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Additionally, I was wondering if it's possible to torrent a copy of the OS, or is it required to download it from the appstore?

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I apologize if these are stupid and searchable questions, but I couldn't find a concrete answer in my brief period of searching.