"I'll go now" doesn't sound quite right. You could say, "I'm (getting) hungry. I'm going to take off. I'll talk to you later." That sounds a little more natural and casual.

Close. In the US, we would say "I am hungry, I'll talk to you later"

Yes. I'd probably say "I'm going to go now because I'm really hungry. Talk to you later."

i feel hungry now. i will talk to you later.

mmm I'm not a native but what about "I'm hungry now see you later" or "I'll call you later"