Remember this about potential pardons.
If Trump pardons someone, they no longer face the threat of prosecution so they cant claim risk of self-incrimination as a reason not to answer questions. In other words, Trump would be removing their right to remain silent on these matters. Theyd still have exposure to a perjury charge.
So pardoning might not be the smartest move here for Trump, which makes it all the more likely hell do it.
That the charge of conspiracy prevents Trump from pardoning. Not sure which is right... just what I saw.
If Trump pardons Manafort, it could only be on the Federal charges. If Manafort faces NY State charges, he could still invoke his Fifth Amendment right against self-incrimination.
Regardless, as you wrote, Trump rarely, if ever, does the smart thing.
Additionally, he can still invoke the fifth if it would incriminate himself on other crimes that he was not charged with.