Do churches vote in pastors too quickly?

I think a lot depends. If you are trying to hire a pastor that is currently a pastor of another church, you can't get too many weeks of "trial sermons" from him.
Time between pastors depends on the situation. You go too long, the interim almost becomes the pastor and him being replaced becomes a sort of church split.

 

The prior church was a member in had the policy that the potential pastor would preach both Sunday services, and would answer questions regarding his doctrines and views, and then be voted upon!

 

>Should a church consider only one candidate as a pastor at a time
or should 2,3 or even 4 men be consider at the same time (top vote becomes pastor)

A pastor friend of mine faced exactly this situation, but the church didn't bother to tell him this was the case. As soon as he found out (just before his trial sermon was coming up), he withdrew from consideration, saying he was not going to be part of a beauty contest.

>How many Sundays should a candidate preach at a church?

Usually one is the norm, since the Pulpit committee should have already heard him in his own church or elsewhere before recommending him to their church. In two different cases, I was brought to a church as candidate for an entire week, preaching two Sundays and one Wednesday. Learned a lot about the church that way, and concluded in one case that no one in their right mind should have to serve there.

>Should the pastor agree 100% to the nth degree with the Constitution/Bylaws?

Strongly recommended that he review such and let the church know if there are any disagreements or issues. If not, these might come back to haunt him later. I had one such situation, and requested a bylaw change, which the church agreed to before I was called.