As I said before the suggested fermentation date is rubbish, that's the company rushing you so that you to buy more kits. You dont need more yeast because even though your current beer is "fermented" there are still trillions of metabolically active cells in the beer cleaning out harsh aeromtic molecules that produce off flavors and triggering lots of chemical reactions you need a full sequence of college Organic Chemistry to understand. Most of that will happen w/ bottle conditioning, but it's far more thorough if the yeast have time to work before the carbonation pressure in the bottle forces them into inactivity.
You don't "have" to boil the syrup for the full time, but there are some changes that occur during the boil which can affect flavor, though if most of the malt got the full treatment the difference will most likely be subtle.
Moral of the story, add the boiled wort, close her up for 3 weeks, open it and do the normal bottling routine, wait 2 weeks, then enjoy great beer!
also @agcorry00 good one XD