No concern, sometimes if you have a real vigorous fermentation it gets done quicker. But Their will probably be some residual fermentables left that still need to be finished. You can take a gravity reading, but I would wait atleast 7-10 days before doing anything to it.
You're fine - even though your airlock stopped, the beer is still fermenting.
The beer can finish fermenting in 3 days, but you should still wait at least 2 weeks before bottling. If the beer hits final gravity quickly, you still need to give it time to clean up any off-flavors made during fermentation.
A few weeks should be ok with a average gravity,did you take an Original gravity reading with a hydrometer?I find it better to let it conditon in primary or with a secondary 3-4 weeks because otherwise it always seems it needs to conditon more in the bottle if i bottle it sooner than 3 weeks anyway.
Also make shure your temps are in the range for the yeast but after a week or so it may be ok to get a little higher to enshure complete fermentation, but with 2 consecutive gravity readings is your safest route for safely bottleing assuming you prime with the correct amount of sugar. I only take one ending gravity reading after about 3 weeks right before bottleing,(if i didnt like that reading or question it i would let it sit for a few more days then check it again- but i have never had to do that yet)and stay within my temps for the yeast and have not had a problem with finished gravitys.Iv'e only used dry yeast also,so far.