They are very similar. I think "on my own" implies "without anyone's help", not just "without anyone's presence".

I think the question-ness of your examples is confusing you as to whether the verb is transitive at all. "Kennen" is transitive. You always have to "kenn" SOMETHING. If your 2nd example were a declarative sentence, it would be "Du kennst den Mann", and Mann is the object of the verb kennen. The article stays "der" in your first and third examples because the verb isn't transitive at all. There isn't some subject that's tasting the salad, or naming the cheese. In fact, der Salat and der Käse ARE the subjects. Does this help?

The phrase "if I know" will never mean "Si, lo sé"/"yes, I know". IF here only means the other kind of "si", the conditional one. Correct sentences: If I know, it is because I heard it on television. If I know you, you'll forget to pay your bills. If I know where I'm going, we should be almost there.

I might favor one over the other depending on context, the first being more abstract: "Hey, guess what! I met a new friend and we have the same birthday!" --and the second being more concrete: "Our birthday is the same day, so we take turns choosing the cake." But really, they are both good sentences and mean the same thing.

It's neither "suwan" nor "sewan". The S and W just run together. Some regional accents in the southeastern USA might make that a two-syllable word, but you're talking about British accents.

Apparently you are one of the ones who think it is. "You've made my mind go wild at first glimpse" is very disrespectful, and inappropriate here.

They are both valid sentences and mean the same thing. I think the second is a bit more formal, and implies more serious thinking about the question. "I'll think about this and give you my decision tomorrow."