I'm new here. First post. Great insights all around.
My reaction to the OP's thoughts are that we have plenty of extraneous pieces we can trade both from the Big Show, as well as the farm.
DON'T KILL ME ON THIS....But as much as Mateo infuriates me with his whiffing on sliders 2 feet off the plate, he has value as a very "weird super sub". I would try to hold onto Mateo unless a team values him a good glove starting SS. He is a top 10 fielding SS and perhaps a top 10 fielding CF. The dude has range in the OF and so much athleticism. He could even platoon with Mullins there against tough LHPs. He also has value as a pinch runner in close games. I would trade Urias wayyyy sooner.
I would trade Santandar, Mullins or Hayes if it helps us secure a SP from Miami, Seattle, or Cleveland who all need hitting. I agree with the OP that a trade has got to be imminent, as it is necessary to clear the OF and IF logjam.
And don't get me started on Ryan McKenna. That was a strange tender decision. I would have non-tendered him if he didn't accept a split majors/miners contract. Minimal power. Does not hit for average. Does not seem to have any upside. Takes away at bats from our top prospects.