I do complexes/circuits now on the same days that I lift. They're great for warm-ups and some cardio rather than getting on the treadmill or walking around the block or whatever.

As circuits go, there's really no difference between body weight, kettlebells or dumbbells because the goal is low weight/high(er) reps back-to-back-to-back with breaks only between sets of circuits.

My dumbbell circuit actually includes angled push-ups and sitting pull-ups, so you can really mix and match things. The best way to design a circuit is to string exercises in a way that the circuit flows somewhat smoothly rather than come to a screeching halt.

As far as too much ... you're going to have to let your body and fitness level be your guide.

I was terribly deconditioned, so I took a month off lifting progression to focus on circuits/endurance while still somewhat maintaining my heavy lifting strength gains, and just this month am integrating circuits and lifting on the same days as my next step to train endurance and strength together. But I'm fine making strength gains slower and don't let some spreadsheet or phone app tell me what kinds of weights to put on the bar and how quickly to progress. Whichever program you follow should be subject to your goals, not the other way around.

My kettlebells and dumbbells are around the 8-10 lb range, so super light weight. Obviously I'm going to increase the reps rather than weight on those because the goal is endurance here, not strength gains.That's what the barbells are for.

Lemme tell you what though, I'm sore today like nobody's business. I've definitely upped the ante by combining complexes and lifting sessions, but hey, my body is responding and the soreness will fade, just like it always does. Today is rest day for me, and that means "rest", rather than getting in any other type of exercise.

I tried doing circuits on rest days and it really wasn't working for me. They would just make my lifts go to crap, honestly, which is why I'm now doing them on lifting days. You could just start with a beginner circuit of super low weights and like 5 reps per set, and see where that gets you. Better to start slower and adjust upwards if you find that you can do more, than to start too aggressive and be sidelined. Just my humble opinion.

I'm doing a variation of Starting Strength and actually 3 different complexes ... KB, BB and DB, strewn about my lifting sessions in a way that is (hopefully) synergistic rather than prohibitive. For example, my BB complex has Romanian deadlifts, which means I do those on non-deadlift days. And so forth.

I chose 3x5 rather than 5x5 because of time constraints and also the sheer amount of work. Right now my complexes consist of 6 or so exercises for 8 reps each, with 2 rounds. So very basic stuff and only takes about 10 or so minutes. Then I do a farmer's walk and get to lifting, which at 3x5 takes about another 20 minutes, and voila, done.

Gonna try it for a month, see where I'm at, and at that point decide if I have it in me to go to 5x5 or crank up the complex volume. I also cut my yoga session short(er) so that the whole workout doesn't take more than an hour. That's enough for 3 times a week, really. I don't want to end up burned out, but at the same time I do understand that strength training isn't the only game in town and that endurance and flexibility are just as important. So it's this never-ending quest for balance and progress. Keeps things interesting though.

At the end of the day you will have to set priorities and decide what matters most, because unless you want to spend hours upon hours exercising, you're just not going to be able to do it all. The charm of complexes is that they do combine endurance and cardio, and you can choose exercises to work out muscles that the big lifts tend to be neglectful of or that you want to focus on a little more; I'm big on efficiency so that's just win/win in my personal book. For example, I have biceps/triceps isolation built in with my dumbbell complex and calf raises in my barbell complex. Cause hey, why not?

I will tell you, though, that 5x5 while starting off (semi-)short and sweet, will get time intensive later on as you'll be concerning yourself with a greater amount of warm-up sets plus greater resting intervals between sets, so just FYI. That's 6 added sets per workout session (if my math doesn't fail me) versus 3x5, which can really add up. But, at that point, you always have to option to go to 3x5, so no harm done, really.