That probably would have killed him even faster yes. Usually with crucifixions people weren’t nailed but tied to the cross with ropes.

Yes, it makes it harder to both inhale and exhale because it makes it difficult to expand or compress your chest since your whole body weight is keeping it stretched.

Basically, once your feet/legs get too tired to carry your weight you hang from your arms. This basically means to breathe you have to push up your entire body weight with your chest muscles. After a while you get too exhausted to breathe and suffocate.

Crucifixion didn’t lead to death by starvation but by suffocation.