Yeah man, I think you’ve got it. Instead of a bunch of sets of a bunch of lifts you really focus your effort on and bust ass fewer reps on a few lifts.
So for your “bench press” you might do 2 or maybe 3 progressively heavy “warm up” or “preparation” sets to get ready and find a good working weight. Then 1 or 2 “work sets” or “money sets” that you keep track of and try to beat next time. After that move to your next exercise.
Switching up exercises is a personal preference thing. I like to make little adjustments (switching from flies to pec deck, or incline barbell press to incline dumbbell press) every 3 weeks or so.
Alternating lifts week to week, like going back and forth between barbell and dumbbell bench press like you mentioned is a pretty cool method too. In think you can go longer, 6-8 weeks between changes if you’re working in a little variety that way.
Some guys don’t like changes or mixing things up. They’re more into finding some good stuff and then just sticking with it.
I guess like everything else, you’ll need to figure out what you like. If things are going well, you’re making progress and the lift feels good you wouldn’t want to change things up just because the calendar said to. On the other hand, if skull crushers are killing your elbows, don’t tough it out on something that’s messing you up. Find a lift that fits you better.