Each and every pardon that is given before the investigation can be completed or before an individual can be indicted and put on trial would be a count of Obstruction of Justice against Trump himself, so I don't think that it is very likely that Trump will pardon anyone at this point. Also, keep in mind if you accept a pardon, legally speaking, it is considered an admission of guilt. It just negates the punishment. That would impact types of licenses going forward that Trump and his family needs to operate their business such as but not limited to liquor and or gaming licenses. Also, it would be damn hard to get commercial bank loans in this country as banks don't lend money to people with a history of engaging in illegal activity.
As to firing Mueller, it makes no legal sense to do so. 1. His investigation is already too far along. If Mueller already has evidence developed implicating people in criminal activity, the Justice Department can't simply ignore it even if Mueller is gone. There are also probably sealed indictments out there floating around. 2. Firing Mueller would be obstruction of Justice. 3. You still have the issue of two more separate ongoing criminal investigations one under Federal jurisdiction in SDNY and the other under the jurisdiction of the State of New York. Firing Mueller would not impact either of those as he isn't in charge of them. And if state charges are brought in NY, Trump would be powerless to pardon anyone charged in those.
As I said before, I think the rubber will meet the road when Mueller indicts one of Trump's family members (Don Jr, Eric, Kushner and/or Ivanka) as it will force Trump to do something and or cause him to have a mental meltdown given how unstable he is. I don't see how Don Jr. avoids indictment as he is the one that arranged the Trump Tower meeting with the Russians, lied about it and he also corresponded with wikileaks. Don Jr has not been interviewed by Mueller which indicates he is a target. I also suspect that is why Don Jr.and his wife moved up their divorce and his wife hired a well known criminal defense attorney rather than a divorce lawyer to work out the details of the settlement. (To try an get a division of assets done in a way that the Feds can't seize her share down the road.)