I agree, the gameplay is smoother somehow, specially when compared to Peace Walker, in which was really hard to pull out some stuff. I want to do some ninja playthroughs like yours (not killing anyone), but some side missions are reaaaaaaaaaally hard, we will see.
The extra stuff, as you said, will take forever to collect, but I will try my best.
Yeah no-kill playthroughs are pretty tough especially when you're trying to get no alerts on top of that (and on the mission that takes place on broad daylight), but when you pull it off its the best feeling ever and thats when the game truly shines.
I really want to get all the extra casettes because I listened to Paz's diary and it was fantastic and gave a lot of back story as well. I'm hoping the other casettes that can be collected are just as good.
Have you tried importing music into the game? Its a very unexpected yet hilarious feature if you set a custom song to play when your helicopter touches down.