Hey,
Welcome to the Skyland club! Great watch.
That large second hand is your chrono hand to measure seconds. Your'e right, the smaller one in the sub dial is the "true" seconds hand.
I'm pretty positve there has been a thread about the effect of running the chrono continously. You could try the search function. But from memory (always a little faulty!) the answer was that extra wear and tear wasn't a particularly great issue. The main thing that degrades in a watch is the lubricant, not the gears. They are designed to run, after all.
In terms of "killing the power", your reserve will drop a little, but only something like 2-6 hours out a 42 hr reserve. If you wear the watch daily, it's never likely to affect it.
Certainly you would want to run the chrono for a short period of time regularly. Moving parts do best when they move regularly. I often run the chrono for around 6 hours. i like to start it when the second hour gets to 30. There's something cool about the second hand and the chrono hand chasing each other around the dial!
Greg