What's the difference between tetapi and tapi? Is tetapi more polite?
"Tetapi" is the standard spelling.
Can you say aku tidak.... and then at the end of the sentence say saya minum anggur. Or doesn't that make sence?
You mean, mix up the use of "aku" and "saya"? Sure, people do it all the time. But in a formal text, it's better to be consistent.