Red Sox have the pieces to make many deals - just a matter of whether its worth it. For Kluber, it is a lot more justifiable than for others. I noted in the past that I would have called the Mariners after 2013 to see what it would have taken for King Felix, but clearly there are a lot of job pressures there preventing that.
Now, as far as guys to give up. I'd consider Betts and Bogaerts - if not untouchable, at least touchable for a lot. If the org is convinced that Vasquez' TJ surgery did its job, then Swihart is somebody who can be dealt in the right trade, and probably would have to be. Margot is tradeable and should garner quite a bit because of his high floor. Devers and Moncada are tradeable because both are far from Boston - but both (Devers particularly) gives the sense of the sort of guy who will embarass the GM who trades him.
Every pitcher in the org is tradeable save for Rodriguez. The org's lack of top end pitching has been essentially a result of not being in the position to draft it - as well as yes, not having the sort of organizational core competency the Cardinals seem to show there (or the Marlins) developmentwise. But it's more the drafting than anything else - have chosen more college pitchers with mid-rotation ceilings. Clearly the org has had hesitation with drafting prep arms in the draft positions they have enjoyed - and those are the guys often who have the star sort of upside.
Rodriguez clearly has #1 sort of things ... this season the rawness as well as the "one bad inning" thing have reared their heads, but he is young enough to work through that stuff. Trading him would be a bad idea in general. (not that there is not a trade where it would make sense, I have trouble thinking of ones that would be plausible though)