I think the obvious outcome of Trump pardoning himself for any and all crimes he may have committed against the United States would carry a very obvious outcome, and implictation - all subsequent presidents would similarly pardon themselves at the end of their presidency.
That could lead down rather dangerous roads, as each subsequent president tries to get away with more and more.
At the end of that road, if it goes that far, is a dictatorship.
There won't be a dictatorship. The President will never have the ability to unilaterally change the law.
The President also relies on Congress to appropriate funds. Perhaps he can redirect them once they are appropriated, but if Congress refuses to appropriate funds to begin with, then the President has no money to spend.
And ultimately Congress will always have the ability to impeach and remove presidents that they find truly unacceptable.