Yes Brat, high reps with light dumbbells are what I use. This gets the blood flowing and the joints lubricated.
When I do the Cuban press I use dumbbells. I tired it with a 20 pound bar but it locked my shoulders into a plane of movement that just didn't feel right (it actually hurt), even though the weight was less than I use with dumbbells. With dumbbells each shoulder moves independently and just feels better.
Body weight squats and toe raises, pushups, chin between chairs, and other exercises done for 10 minutes (one after the other) usually makes a good warm up for me.
As for your question about working sets, it fluctuates. I've gone as low as 3 sets on the compound exercises and as high as 10. It usually is dependent on my rep range. If reps are 8 to 10 then I use less sets. If they are 3 to 6 then I use more. I tried the ABBH workout that Iain posted a link to and the 10 sets of 3 was a great workout. Also, arms only get 2 or 3 sets, never more. They get a great deal of stimulation from the
compound movements.
One suggestion: 5 x 5 works great if you are going to squat, bench or dip, and row or chin all in the same workout. It is a lot of work to do those exercises in the same workout. Your
energy expenditure will be large. As for DL's, you might want to rotate them with squats. IMO, they both use the hips and glutes as primary movers of the weight.