(1) It's not possible to predict how long it will take to upgrade to captain anywhere. Always keep that in mind--it doesn't matter if anyone tells you it's a sure thing to upgrade in a year. Some regionals were upgrading in 1-3 years, but they aren't now. Amer Eagle's most recent upgrades took 8 years. I doubt if the future will see any 1-2 year upgrades anywhere for a while. The biggest factor in shortening upgrade time is whether an airline is growing and thus needing more pilots. Regional airlines boomed in the 90's and into the 2000's because more flying was being delegated by the majors. That's not really true anymore, so places like Skywest are losing flying instead of gaining it, which means the seniority list is pretty stagnant. Also, many regionals require you to have a certain amount of hours before you can be a captain, so even if the list is moving fast, you may need to wait until you have a few thousand hours anyway. The picture is not looking rosy right now, and personally I doubt it will get much better any time in the next few years, especially with the new age 65 rule.
(2)If you change airlines or get hired by a major, you absolutely are straight to the bottom, doesn't matter if you're 57 with 90k hours or 22 with 300, you're gonna be the whipping boy and make crap money again.
(3)Impossible to say how long a furlough could last.
(4)Regionals don't care, major airlines do. Are there major airline pilots out there with no degree? Sure, there's a decent amount. But there definitely is no shortage of people who want to be pilots, and you're competing with all of them. This is one reason, among multiple, that it's very important to ask yourself this question before you decide to become an airline pilot: "Could I be happy as a career regional pilot, or do I want to fly 747's?"
(5)Being on reserve means you have a schedule of days where you are on call and days off. Holding a line means you have a schedule of trips and days off. There is a minimum guarantee of paid hours for each. With a line, you know when you're flying and when you're done.