Totally agree on Walker, 1 year at a time at each level. He needs to face a bunch of AAA and AAAA junk ball, off speed pitchers first. Once he gets a steady diet of that, hopefully cuts down on his strike outs, then he should be ready. I also think that possibly one of the reasons for his high so% is his willingness to go deep into the count, waiting for that right pitch that he can clobber and taking a called strike 3 on the couple of games I saw, rather than all swinging strikes.
You may be right on Kepler, keeping him at Chattanooga for the year, see if he can sustain this level of success. Then next year, start him off at AAA and be one of the first call ups. The games I saw him play, he was the most athletic player (excluding Buxton) on the team and man that sweet swing is something, so smooth.
Based on my eye test, all Sano needs is a little more repetitions at 3rd and I'd send him up. He makes tough plays at 3rd but the routine one's are still little inconsistent