Rome and back?
Did half that (which was 100m a day for 14 days) a few years ago. Mostly flat (it was from work to Rome, so sort of following EV5). But, in a group with our bags carried so much easier.
Possible pitfalls: headwinds, injury, loneliness.
Possible benefits: tailwinds, fitness, solitude.
I completed mine and don’t regret doing it despite picking up an injury half way through which has never really ever fixed properly. It reminds me of the achievement.