1: No, absolutely not. If you have played the first game there'll be a few returning characters and easter egg type scenarios, but I think of it sort of like Arcane. If you have played the game(s) before, it will add to the experience, but if you haven't it won't detract. 

2: Oh absolutely. It uses the 5th Edition ruleset as the game's ruleset, but you need absolutely zero knowledge of how D&D works to play the game. Again I'd say it might add to the experience if you do, but if you don't it won't subtract anything effectively. 

3: Nope. Once you download it you're all good, unless of course you want to play a co-op run with a friend.