I would say that both are identical in meaning although one could say that "pyaar" is the every day word for "love" whereas "prem" is perhaps more frequent in the higher register language like "muHabbat" and "3ishq".
No, I would n't. One can say that people would normally associate prem, muHabbat and 3ishq with "true lovers" and "pyaar" with the rest of mortals! But the words themselves mean one and the same thing.
In romantic poetry, you will read/hear all these words implying love.