Good questions with answers below…
(1) How long is a workout? Should it be a half-hour or a full hour?
Depends on your goals and current fitness level. 30 min is great for a beginner / maintenance plan or high intense workout. 60+ min is needed for longer events like marathons, triathlons, spec ops training, but fine for a body building workout. Like I said — all depends…
Mine are usually 2–3 hours long full of calisthenics, running, swimming mix in the summer and shorter with weights and light cardio in the winter — see how
(2) Should each workout be a full-body workout, or is it better to focus on a particular area?
Full body workouts are fine every other day but never back to back to back days. You need 48 hours for optimal muscle recovery but that varies too with intensity, weight, effort, your age, etc…
Personally, it is best to work full body with full body movements not a bunch of isolation machines. the body works with full body movement patterns not a series of isolated joint events. So unless you are a body builder or rehabbing an injury there is no need to do a single joint workout.
It is fine to supplement a few isolation exercises into a full body workout though. I add in bench press, military press and other exercises into workouts where I do hang cleans, push presses, power cleans…etc.
(3) Should workouts be just strength training, or incorporate aerobics as well? Jump-roping for example.
Sure you can do both mixed in sets of pushups, pull-ups, jump rope (1 min each) or you can do all your weights / calisthenics first then do your cardio after. Once again = it is up to your goals, current fitness level and if truly depends on how you like to change it up. I never recommend doing the same old split routine for months at a time. Change it up and add some variety to avoid plateaus in strength gain, weight loss, performance, etc…
Depends on your goals: weight /fat loss? Strength gains? Running or swimming faster?
See how the order affects your goals — http://www.military.com/military-fitness/health/cardio-vs-resistance
(4) How much pt can you do in a day? Not your absolute max, what you can reasonably do without exhausting yourself?
Once again — depends on your fitness level. we do 5 hour events (a few times a year) where you run 4 miles, ruck 4 miles, swim 2 miles and get in 1000 pushups, 1000 abs, 250 pull-ups, and 250 dips. That by the way is too much. I feel this for too long but some of the younger guys can do this and more.
For some people walking a mile and doing 50 crunches and 25 pushups is too much. But if you are training for the military and have a decent fitness foundation, you can do 25–50 pull-ups, 100–200 pushups and sit-ups in a workout period along with a few miles of running and not overdo it.
Fitness is all relative to your goals, current fitness level, and facilities and time you have to train. Find what works best for you and go with it. You cannot argue with results if you are happy and healthy with those results.