I like your ideas. If I may offer an opinion. I know you don't want an entire league vote, which makes sense to me too.
My only suggestion is that you or ez as commissioner make an initial ruling. After that, the league member proposing the trade is allowed a single appeal- if they so desire- in which 3 random and anonymous league members are chosen to chime in on the trade. (again just via a back and forth with you/ez, in an anonymous fashion-PMs) If 100% (3/3) approve the trade, they would win the appeal and the trade would go through, otherwise, the trade is dead.
Just an idea. I know getting an entire league vote would be too much, but this may be a compromise, in the interest of a consensus of sorts.
That's too cumbersome, but if this becomes a problem then maybe.
The league members who are randomly chosen will not be anonymous though.