To answer your first question: The amount of time and effort you put into being a GS leader depends on you. You will need to take training, you will have to hold regular meetings, which can be weekly or twice a month. There are always Moms who are happy to volunteer to lead the girls with earning badges, doing community service work, or being chaperones for field trips. So, you shouldn't be all alone in running the show.
My daughter has been in scouting for nine years, and this is my observation about the various leader she's had. The BEST leaders are the ones who are truly devoted to scouting. They do it because they believe in the GS principles and love seeing girls grow and blossom into capable, compassionate citizens with great leadership skills. These women devote A LOT of time and energy to their troops and consequently have girls who are very enthusiastic and involved.
The worst leaders I've known get into it only because their own daughters need a troop to belong to. They stay in it as long as their daughters are interested, and desert the other girls once their daughters decide to move on. They put in the least amount of time and effort, and the girls in their troops are bored and don't get much out of the experience. We've had both kinds of leaders through the years.
So, please consider carefully your motives for wanting to be a GS leader. If you only want to do it for your daughter, you could be shortchanging the other girls in the troop.