1- It varies with the time of year, but it's pretty cold most of the time. Below freezing (30 degrees F, 0 C) most of the year, with highs in the (quite short) summer hovering between 50 and 60 F. Further north, like the northern parts of the big island and further up, rarely rise above 30 F. So...it's cold, a lot. Considering how in the winter it's dark most of the time, and winter lasts at least half the year. Temps in winter months would be below 0 F much of the time (between 0 and -20 F, with lower temperatures on occasion depending on cold snaps and wind speed...).
Just as a reference, the average temperature in Yakutsk, Siberia, in winter can be as low as -40 F, while as high as 60 F in summer...and more than 200,000 people live there (!!).
And I haven't yet decided when exactly the campaign will start. Not sure yet if I want to be mean and have it be dead winter, or nicer and have it start in summer or fall...
I didn't see rules for this anywhere, but I would rule that within 10 feet of a campfire (or similar source of heat) the temperature band is effectively 2 bands warmer, maybe 3 bands warmer within 5 feet. So you wouldn't freeze to death sitting around in camp...as long as someone remembers to bring a flint and steel or some tindertwigs (or some kind of fire spell) to start a fire, otherwise you'd be in trouble!
2- As a human you choose which class is your favored class. So whenever you take a level in it you get those bonuses. Could be the highest or lowest class.
At least that's how I interpret "favored class: any"...meaning, "favored class: any one of your choice"