They mean the same thing. You can both talk with someone and talk to someone. However, talk to you later is the common colloquialism

Q1: Almost, but not quite. "talk with" has a sense of a more extended, two-way conversation, and perhaps without a single focused goal, although "talk to" certainly can mean this too. Also, in my day at least, I think "talk to" was more common in the UK. Both are used in the US. Q2: Because this is English!

No they aren't exact equivalencies. In native English we would say "talk to you later" and here later has not limitations of time. It could be 1 hour later or 1 year later."Talk with you later" is never used in English in almost all forms. When using "with" in reference to conversation we would nearly always say "speak" rather than talk. So "I will speak with you later". This is quite formal, and again rarely used. More commonly I use the phrase "I will speak with (person) about that" in formal business speak

Yeah, I agree with James. "Talk to you" is used A LOT, but I like "talk with you" better because it seems to suggest more of a dialog between two persons. "Talk to you" seems more one-sided, as if you are lecturing someone or giving orders. But both are acceptable and understood to imply roughly the same thing.