That is a very old rifle. According to Brophy it was probably made in 1905 and is definitely a casehardened low number action.
NS on the bolt stands for Nickel Steel and is a replacment made in 1928 or later.
Maybe. It might fragment if a casehead split. It might not.
P.O. Ackley said that the bolts were more variable than the receivers and that he considered a low number receiver with a nickel bolt to be safe to fire with standard ammunition. But there are more lawyers in circulation now and it is usually recommended not to shoot a low number Springfield. I have shot one and am still here to tell it, but I am not telling you to shoot one I haven't seen.
Since the bolt is certainly a replacment, headspace could be anything. If replaced by Ordnance or a reputable gunsmith going on Ackley's advice it would be correct, if stuck in to complete a bubbaized parts gun, it could be anything. The only certain way to check headspace is with a headspace gauge used correctly. Technique matters.
Y'all be careful, now, you hear.