Hi, JES. One issue is if the ends of the boards are cut for tongue & grooves also. If they are, you will have to route the ends. If not, you might want to back cut about 5 degrees on the end if you can. Your chances of good tight joints on the ends will be much improved.
If you have random length boards, the easiest way is to "pipeline" the boards and get the joints in random locations. Just cut the first piece so it ends over a joist and nail up that piece, cut the next piece to fit the opening, then start the next row by coming back the other way with the cut off piece as long as it is a couple of feet long and can be cut to reach to a joist.
I'm sure that you can work to a pattern for the joints but you will use a lot more wood and have to make a lot more cuts and joints.