I would say one mile.
No clue
They've actually extended the river walk from 13th Street bridge now so it's from there to the Marina. If you want something a little longer you should look into the canal or the walking path by riverwatch parkway it runs from behind lake Olmsted stadium to 15th Street.
Long Enough to enjoy, have a romantic night walk or daytime. Enough to get tired, have a good exercise. It's best to go and experience it and find out in person.
Probably a good half a mile
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