I think you can break it down into three categories -- What Trump thinks, what his legal team is arguing, and what the law actually provides.
Trump no doubt thinks that while he is in office he is basically immune, and that if necessary he can give himself a get out of jail free card by pardoning himself. Personally I think that if he tests that, he's going to be sadly mistaken.
I think Trump's legal team is arguing that while still in office Trump can't be indicted, subpoenaed or compelled to testify. The remedy is to impeach him. The unspoken part of that argument is that once he is out of office, he may very well be indicted, subpoenaed or compelled to testify, and can be successfully prosecuted unless he is pardoned.
I suspect, but don't know for certain, that the law will go this way:
Indictment and prosecution -- Have to wait until impeached, resigns or term runs out.
Compelled to testify, respond to subpoenas -- May depend upon whether the act occurred before taking office or after. I think the Clinton case resulted in a ruling that for acts that occurred before taking office a president can be questioned, which lead to Clinton's deposition. I think it's still an open question about whether the president can be questioned or compelled to answer a subpoena about acts that occurred while in office, until he is impeached, resigns or his term runs out. At that point he's fair game.
Once the president is out of office, he can be indicted and prosecuted for any matter that occurred while in office or while out of office, unless he is pardoned. I don't think a president can successfully pardon himself.