Perjury is perjury, whether you lie to Congress, or in court, or to federal investigators. This is another one of Mueller's brilliant moves: He waits until Trump claims in writing and under penalty of perjury that he had no business dealings with Russians after he became President, and then has Cohen admit in court that he did. No doubt there is documentary evidence to back that up. That is Mueller's style: Use the documents to convince somebody to flip. Then you have both documents and people involved with the crime to take to court.
And I think it's a sure thing that Trump made provable false statements in his question reply. He'd have to admit everything to make his answers true, even if he avoided some topics. We can assume Mueller knew the answer to every question in great detail before he asked them. Any good prosecutor does.
As to who will prosecute Trump? New York state AG, that's who. Most of his federal crimes are also state crimes. Do you honestly think the state of New York is willing to forego collecting Trump's ill-gotten gains? The day he leaves office, New York state tax forensic accountants will be all over his finances. His only hope is to drop dead or flee the country before then.