Thanks!
3 - yes, I assume as in "yes, you are right" not in "yes, change those"
CTR? Datasheet of the optoisolator, right? Doesn't have any CTR mentioned. MIDI specs don't have any explanation on that part either.
So that resistor is basically a limiting resistor and derived from current being supplied (so "strong current" will be determined by some spec of optoisolator)? Alternatively, I guess, I can find schematics for 5v powered optoisolator and use ~0.66 amount of resistance?