If P = NP were proved to be true, it would tell us that there are solutions to a certain class of problems. Assuming it's true doesn't give us those solutions.
Wikipedia should answer most of your questions regarding the consequences:
To be a little more precise, proving P=NP would mean that there are algorithms to solve those problems that take polynomial time (can be calculated with a polynomial).
NP problems can be solved, it's just slow (think brute force method, running through all the possibilities).
Not true. A polynomial time algorithm for NP complete programs is known (if P=NP that is). You just need to prove P=NP to prove that it is polynomial time.
Wikipedia should answer most of your questions regarding the consequences:
http://en.wikipedia.org/wiki/P_%3D_NP#Consequences_of_proof