Right on both counts. The minimum load impedance of the concert Lead is 4 ohms. As long as the total impedance of the cabinets you use is 4 ohms or greater, you and the amp will be fine. Your cabinet is 16 ohms, so that's fine. You should be aware, though, that you'll be getting only about 50 watts output at that impedance.
Using the preamp out/power amp in as an effects loop should be fine, as long as the effects can handle the line level signal.