Accidental death is ~50/100k/lifetime. So 0.9995^n = 1/2 is our accidental halflife. Works out to about 100,000 years on average. Someone please check;)
Of course it's not just accidents we'd need to worry about if we didn't age — there's also murder, warfare, suicide, infectious diseases, etc. I think Aubrey de Grey said the average lifespan would be ~500-1000 years absent age-related diseases.
I think people's risk tolerances would dramatically change with unbounded lifespans, and we would take any threat to life much more seriously than we do now.
For a while yes. Though I can imagine very old but fit people taking up extreme sports when they get bored with life and dying in entirely avoidable accidents.
The probability to get murdered in a lifetime is already higher than that (a little bit higher in Europe, a lot higher in US).