I'm not a professional but I did a lot of research before buying the winter tires I have (I put the same ones on my wife's car)
-Knowing that longevity is important to me (I don't want to buy a new set of winter tires every other year), are there any brands/styles you can recommend?
The Continental ExtremeWinterContact tires I bought seemed to do better than other snow tires in terms of longevity from reading reviews. The Tire Rack has a tool that will show you what winter tires fit and many users submit reviews detailing tread life, performance, comfort, etc.
-Will highway driving on salty roads greatly diminish the life of my winter tires?
Not sure, I've only driven in the snow in the Midwest.
-When would you recommend switching into and out of my winter set of tires each year, and why?
It depends on your preference. I remember reading somewhere "when the average temperature drops below 45 degrees Fahrenheit. I'm putting mine on in about a month since we get snow before Halloween. I took them off mid April and we got hit with an ice storm a few weeks later. I'll probably put them on mid Oct and take them off mid April this year too.
-Should winter tires only be used below a certain outdoor temperature or speed in order to prevent premature wear?
The tread compound on winter tires is much softer than all season tires, cold makes it less soft. If you leave them on well into the spring expect premature wear (as my friend who left them on through June found out, bald blizzaks after 6 months).
That being said, I put the winter tires on my wife's Accord early Oct while there were still some warm day and took them off mid April. They show little wear. On my Focus I put them on in January (bought the car in Dec) and took them off mid April and they show no wear.
I hope this helps some, the Tire Rack sales rep can probably help more. Remember your ABS doesn't help you stop, it just helps you maintain control while trying to stop. The traction control doesn't give you extra traction, it just prevents you from sending too much torque to the drive wheels (which may sometimes be any at all).