Yes you can. When played as sprint cards, you ignore the number and only count the footsteps on them.
There is a risk though that if you use too many high numbered cards as sprints you will be unable to get to your escape plane as there will be too many gaps in the high order hideouts.
This is correct. Sprint cards can be any number, all that matters is 1 footprint or 2 (Odd #'d cards have 1 footprint, even have 2, in case that matters to you).
He is correct there is a risk too. You can use some of the cards you get to bluff easily, but bluff too much and you'll have to stand still for a while sometimes, which is very risky.