Suppose you have an object accelerating due to a force $F$. Then, you apply the same force in opposite direction, $-F$. There is no net force, so obeying Newton's first law it will move at constant velocity. So the answer to your first question is yes.
As you guessed, you should apply an additional force to stop it. Of course, you must apply this force only until it stops.
Yes, when accounting for factors such as air resistance and biological processes, there is clearly energy used, and work being done somewhere.
If you're only considering a book moving at a constant velocity in the horizontal direction, you could say there is no net work done on the book.
If we analyze it further, you will find that if it moves with a constant velocity, there must be some other force acting on it to counteract the drag force. This is the force supplied by you when moving the book.
If this book is moving with constant velocity, this must mean that the net force acting on the book in the horizontal direction is $0$. If that is the case, the net work in the horizontal direction required to keep it moving at the horizontal velocity is zero. The work done by the person on the book is exactly countered by the work done by the air resistance on the book, and thus no net work.
Work is required for a person to move a book through the air at a constant velocity, because the work done by air resistance needs to be countered, but the net work on the book during that movement is none.
It's also often the case that it's assumed you can neglect air resistance. In that case, it would not require work to keep the book moving at a constant velocity. I suspect they may be making that assumption when they are discussing work.
You could also consider a situation where you are starting from a standstill, and ending at a standstill while covering some distance. You can see there is work done to accelerate and decelerate the book. From an energy/work perspective, the work required to slow down the book is exactly opposite of the work required to get it up to the moving speed. This also means that no net work is done on the book during the entire travel (though both the person and the air will have had net work done on them).
Best Answer
It's not easy pushing something with by hand with a constant force greater than kinetic friction.
Try using a rubber band and a ruler to pull something across the table with a constant force. I think if you focus on keeping the rubber band stretched a constant amount while you pull you will notice the object will accelerate.