To answer your question. Put the floor in first.
This will save you alot of trouble, and alot of quarter round.
Second. Not that you asked, but why? armstrong? Armstrong swiftlock to me is junk. Pergo will go down much easier.
If you are intent on armstrong, and cannot return it for some reason , this is what you will need.
Most of the locking mechinisms will not come together, so you will have to hand plain the edges. This is best acheived with a very small hand plain. (sometimes you will have to take the edge off of the plank all together.)