Martin. Weather: The Lake Chapala area is about the best in the world (despite a little colder winter and warmer summer this year). Mazatlan, PV, Manzanillo have great winters, but watch the hot months (July,Aug/Sept.) If you are not used to humid and heat, you will be miserable.
A lot of people do have a summer home and a winter home.
Contact forums in the cities you are interested in or google the cities for additional info. The cities I like on your list to explore ate Mazatlan, Lake Chapala area, Guadalajara and VP (real expensive). If you want small cities, try the array of Pacific coast cities between Manzanillo to Mazatlan. I personally do not like anything in the Baja, but some do. Mexico offers a large variety and you have to seek out what you want. What are your priorities in a place to live (weather, cost of living, activities, culture, etc)? Good hunting. EEK!