First off, I hope you're doing more than just the 5 exercises in the article you linked to. Those exercises are indeed a good set of exercises for the upper back, but good posture is only achieved through exercising the entire body!
Intensity and volume parameters
When deciding your set/rep ranges, one often asks "do I want to focus on strength, or size?" Naturally, in most cases, focusing on one, will lead to improvements in the other.
As a rule of thumb, we like to divide the rep ranges into 3 basic stages;
- 3-5 reps with high intensity for strength gains
- 8-12 reps with mid intensity for size gains
- 15+ reps with low intensity for stamina/endurance gains
Again, this is a rule of thumb, but it's a place to start. For the rep ranges in between, you can probably guess what's going on there. It's not like you're getting "the best of both worlds" by going with 6-rep sets, but it's not like we discourage their use.
For posture, I'd suggest 8-12 reps per set, for 3 sets.
This study suggests that if one is aiming for hypertrophy (size gains), doing more than 2-3 sets provides very little benefit. Most of it is achieved through the first 3 sets. I've adopted this tip into my own training with good results as well, just to throw some anecdotal evidence into the mix.
The best tip for good posture
I would be a bad advice-giver if I didn't say this. If you want good posture, do the big compound movements. A compound movement is an exercise which engages a large set of muscles.
Deadlift is widely regarded as the #1 exercise, and belongs in any exercise regimen. It works lower back, legs, upper back, shoulders, neck, forearms... The list goes on.
While I like to draw the deadlift out as the biggest posture exercise, the other compound movements you absolutely should be doing are;
- Bench press
- Pullups and barbell rows
If you're a beginner to weight training, it's OK to split these up into two groups, and alternate them between training days. Likely, you'll want to have deadlifts and squats on two separate days because they work a lot of the same muscles. If you do one first, you'll likely be too exhausted to perform very well on the other.
Rest period for muscles
This is another rule of thumb, but it's a widely accepted one; give each muscles 48 hours to recuperate before working it again.
As with any rule of thumb in working out, it's a place to start. It's up to you to experiment, and figure out what works best for you. If at any point you're in doubt, the rule of thumb has your back.
If you feel like you can do deadlift one day, and squat perfectly the next, go for it. But if at any point you feel like you're getting fatigued, and can't quite understand why, it might be because of the short rest periods you give yourself. Just something to keep in mind.
An example of a program
Since this became a bit of a wall-of-text anyway, might as well.
Day 1: Squats, bench press, pullups, +++
Day 2: Deadlift, barbell row, dips, +++
For the +++ part, you can add some movements of your own choosing, like the ones from the article you linked. Like I said, they're not bad exercises, but those alone won't do the trick.
Then just alternate these two days.
For some variety, you can easily mix up the order in which you do these movements. For instance, next time you do day 1, do pullups first.
For any of these days, I would advise that you do the compounds first, and then move on to the smaller ones. That said, I have seen examples of extraordinary athletes who do isolation (opposite of compound) exercises first, and then compound movements later, because they want to do them while already fatigued.
This is pretty much the advice I would give any and all worker outers who are unsure of where to start, whether it be for posture, strength, size, or any combination of these. And of course, feel free to ask about anything I missed.
To answer questions in comments below:
1) The reason for suggesting 8-12 reps per set is that for beginners, your posture will inevitably improve no matter what range you choose. And since the article you mentioned offers tips on the V-shaped back, size training is going to further facilitate this.
2) Avoiding chest exercises is not a solution to the seated lifestyle. To avoid posture issues from sitting a lot, you should do stretching. When you're seated, slouched over a desk, your muscles tense up. Not working out these muscles doesn't solve anything. You're just leaving it alone to get worse. Stretching is the solution here, because it increases the flexibility of your muscle fibres. Not only does it prevent injury from weighted resistance, but it also prevents the slowly-but-surely achieved injury from sitting all day. As a web developer by day, and avid gym-goer by night, I give stretching credit for my corrected posture.
Long story short, don't neglect any part of your body. Strengthen it, and stretch it! Besides, posture isn't back only.
3) Neither a trainer nor myself should be giving you advice on how to deal with kyphosis. You should consult a doctor about this. If you simply can't do deadlift, there are exercises which, combined, can add up to much of the same benefits as the deadlift. Squats being the first and foremost of them.
4) Posture starts at the legs. There's a trend within the fitness community, where people make fun of those who have a large, lean, good-looking upper body, but untrained legs. While this is mostly light-hearted joking around, there is an underlying point to be made here. How do you expect to have good posture if you have weak legs?
And like the point about the chest; working out only portions of your body is going to lead to muscular imbalances in the posterior chain, which is really, really harmful and posture-destroying.