Rather than talking about positions, how about categorizing the possible trades by contract?
a) Expiring contract--Free agent at the conclusion of 2021. Cruz, Simmons, Happ, Shoemaker, Robles, Pineda, Columé
b) Free agent in 2023--Expensive to re-sign. Trade if not extended. Buxton, Berríos, Rogers
c) Under contract but team has a likely replacement--Sanó, Polanco, Kepler, Arraez
I wouldn't expect all of those guys to be traded. In fact, in both b and c, probably no more than one could be dealt. It seems to me that the pieces of the roster have never fit together properly from the position player side and the pitching is simply short on talent.
I think factors in trading players include whether they are more valuable to the current team they are on and also what the market is for a player in their position and role. Of course, the return received should be commensurate with the value they provide to the acquiring team.