This sounds crazy, because for me to say, "Hey, ignore those instructions and do what I say, because you met me on the internet" really doesn't sound very positive............but I really can help you on this because I have done this exact thing more than once.
1. Yes! And because condensed sugar solutions darken more than water solutions, I'd add only one can of the extract or the one bag, whichever. That doesn't really matter. The idea is to avoid excess maillard reactions (similar to caramelization) that would darken your wort excessively and lead to an "overcooked extract" taste instead of beer taste.
2. Yep, and start the timer when you add the hops. When you reach a boil, start the timer and add your hops.
3. Yes, add them as instructed.
4. Add them after you turn off the flame, when your timer hits "0". If you add it at 15,5, etc, you'll just stop the boil for about 10 minutes and there is no reason to add it then. Turn off the heat, and add the extract off the flame and stir well. It's still plenty hot to pasteurize the extract plus won't impact your boil.
Many "modern" kits have the instructions adding the bulk of the extract at the end of the boil, so it's not anything new or weird. Extract has already been processed by the manufacturer so it doesn't need further boiling or other processing. It will keep the color lighter and tasting more like beer made out of grain than beer made out of malt extract.
