1-arm elbow out rows, 3-4x8-12, powerful positive and a slow-ish negative. Focus on keeping the elbow in line with the shoulder, or even slightly more forwards.
And 1-arm standing reverse cable flyes, 2-3x10-15, touching the working muscle with the fingers of the non-working hand and shortening the ROM to eliminate the first portion where there's least resistance.
Basically this ^ (no, that's not me, hardy har har), but i'd set the pulley a notch or two lower, so it's actually level with the shoulders, and the dude's left hand would be feeling the right rear delt working (tough to find, but get it in place before the set starts). You'd only "lower" the weight until the right hand is about even with your face. Sounds more complicated than it actually is.
Yep. Never a bad idea.
Also never a bad idea. Band pull-aparts are one of the few things that almost don't count as "training", but at the same time, can have a big impact in the long run. I have a simple bungee cord I keep around the house to knock out some whenever.