I think it is important not to stretch the long arm of possibilities out of socket. First, the only video that has been associated with this case is one that Russian intelligence may have made of Trump in a hotel room, watching some prostitutes engaging in the art of urination. There is zero chance that if such a tape does exist, that Putin has shared it with US intelligence and/or the Department of Justice.
Michael Cohen did tape some phone conversations with Trump, one of which his attorney has made public. These are being held by the Southern District of New York. It is likely that Mr. Mueller's team has heard them, and possibly obtained copies. As acting Attorney General, Whitaker could in fact ask to listen to them, as part of evaluating the SDNY's cases, as part of supervising them. However, there is zero chance that he could obtain copies. More, as the SDNY possesses the tapes, there is absolutely no chance that Whitaker could somehow use them to blackmail Trump. None.
Trump infamously claimed that President Obama "wire-tapped" him at Trump Towers. Besides exposing the surprising degree of ignorance that Trump has regarding modern methods, this shows an even greater degree of paranoia. We should never share these paranoid conspiracy fantasies of Trump.
Likewise, Whitaker could view the files of Mr. Mueller and the SDNY, but could in no way whatsoever have "office copies" -- much less personal copies -- of them. Again, as they are firmly, 100% in the possession of Team Mueller and the SDNY, there is zero chance of them being used to blackmail Trump for a pardon. As much damage as Trump has done to various institutions, including DoJ and the FBI, it's essential that we remain reality-based, and have an understanding of how things actually are conducted.
Finally, I think people should understand that Trump doesn't have that much cash, on hand or otherwise. One of the major reasons Trump's initial legal team quit was because they were not being paid. His current legal bills are draining his available resources. It is essential that we stick to actual facts. The current reality already reads like a horrible movie script. No need to add what isn't real.