Yes, your front leg can be slightly bent with the restriction that you gain no advantage from a springing action.

Yes

No. The average speed needed to complete 100 miles in 24 hours is 6.71 kilometres per hour which is just one kilometre per hour faster than the average speed of people walking in the street.

• Stamina: you need this to walk 100 miles.
• Determination: of the people who have achieved centurion status, all but the very fit felt tired at some point during the 100 miles. Determination got them through.
• Pace judgement: the more variable your pace during the 24 hours, the less distance you are likely to cover.

This can happen to people running 24 hour race, but we have never heard of it happening to someone walking a 24 hour race. Runners who have reported hallucinations have found the hallucinations go away after a short rest.