Belgian Tripel: Fermenting and additional yeast?

One week ago, I just brewed my first batch from an extract kit of "Brewers Best" Belgian Tripel. The recipe recommends 1 week of primary fermentation, 2 weeks of secondary fermentation, and 2 weeks of bottle carbonating. (Despite the recipe, I have heard some sources recommending to ferment in the secondary for 3 weeks or even 2 months.) Also, the recipe estimates the F.G. reading to be near 1.02. Before fermenting, I took an O.G. reading of 1.09.

Today, I just siphoned the Belgian Tripel into the secondary fermenter. Also took an S.G. reading of 1.02. Since the S.G. is showing that it the fermentation is already about complete, will secondary fermentation have any impact? If so, any recommendations how long?

Also, I heard that during bottling when priming sugar is added, the yeast will eat the sugar in the bottle to produce carbonation. Given the fermentation time can last long, will this affect how many yeast are still alive? If fermentation times last long, any recommendations on adding more yeast?

I'd appreciate any feedback if possible.

Your Tripel shouldn't really be fermenting anymore if you're at 1.02, or it should be very nearly done. The point of it being in the secondary is more to help clear the beer and condition it, letting the yeast clean up some of its byproducts. A lot of people around here don't move to secondary, instead just opting for a 3-4 week primary fermentation. Since it's in the secondary now though, I would give it 2-3 weeks or more before bottling.

As far as carbonation in the bottle goes, unless you leave your beer in the fermenting vessel for several months, there should be enough yeast in suspension to properly carbonate/bottle condition. I've bottled an ale that was in the primary for over 6 weeks and did not add fresh yeast, it carbonated just fine.

Hope this helps, and welcome to the hobby!