In a span of a 1-hour workout, how much cardio and strength training should be done?

Quite a lot can be accomplished. But to answer the question, how much "should" you do? You want to make that hour count. There is no need to hold back or limit your effort. The body can take a lot, and an hour is a reasonable window in which to push yourself.

My best advice for maximizing an hour of training is to incorporate rest-pause training. This involves restricting rest in between resistance training sets. The benefits are:

  1. More engaging workouts.
  2. Shorter, but still effective and intense muscle building workouts.
  3. Elevated heart rate, so resistance training also acts as a secondary form of cardio.
  4. More brief workouts.

You can accomplish a lot during a 40–45 minute rest-pause resistance training session. This leaves room for HIIT cardio, which is your best bet when limited in workout time.

Read more about HIIT cardio here. If you are look for a good rest-pause workout example, try my block training program:

How often should you stretch to increase flexibility?

Minimum is 2 days a week.Crucial to maintaining joint range of movement, completing a series of flexibility exercises for each the major muscle-tendon groups (a total of 60 s per exercise) on ≥2 d·wk is recommended.Source: Quantity and

I have a pair of adjustable dumbbells, a barbell, weight plates, an adjustable bench (without any rack). How do I get the most out of it for bodybuilding?

Oh man, you definitely have enough to succeed with that.  This is what I would do in your situation.Progress in strength on deadlifts, overhead press, and front squats (all can be loaded without a rack).  Keep the rep range relatively low