Ambi: If you are interested about these things, I suggest you google the web for a document titled "Handgun Wounding Factors and Effectiveness". It is a USA Government FBI paper that presents the results of the FBI's study of handguns for its agents after an incident in 1986, when two men armed with rifles, handguns, and protected with body armor went on a rampage. Law enforcement had a terrible time getting this situation under control. Therefore, they began a study of what actually was needed to immobilize an attacker in future situations.
The bottom line to this, as you will see if you read the paper, is that a minimum of 305 mm of penetration is required to effectively and reliably disable an attacker. You realize that notions like "shoot him in the knee" may not disable an attacker, and extremities are a much harder target to hit. Brain, central nervous system, and cardio type shots are what's needed, the same as any big game hunter knows.
An ocean of ink has been spilled on this subject, but the scientific and concise paper I've recommended hits the high points and will start your thinking process down the right avenue. Then, you have a basis to consider other aspects of this matter.
When you consider bird shot and other small pellet sizes, consider how well you think that they might meet the 305 mm requirement -- clearly, they will not. As a matter of fact, I knew an individual who got involved in a store robbery and cut loose on the armed robber with a shotgun loaded with #6. The robber was a little bothered, but hardly immobilized or stopped by being hit.
There is debate about a shotgun load, but most folks who know seem to consider buckshot or a slug to be proper for self-defense. Buckshot, especially in the larger sizes, can retain enough energy at close range to arrest an attacker's evil intentions. However, in your situation, you may find a shotgun somewhat cumbersom for your purposes.
I'm not familiar with the legality of sawed off shotguns, such as what's in the picture you have posted. Someone else will need to discuss that issue. But I would ask, are you actually going to try to carry such a thing? How will you conceal it, especially in warm weather, when you have light clothing? Another thing to think about is actually shooting something like that. Have you tried touching off a shotgun held with one hand? You may find it an interesting experience.
"firing warning shots"
What will the police think of you firing "warning shots"? What will you do if a goonda claims you were trying to murder him? As I've mentioned, how can where the bullet lands be known?
"shooting to wound"
If it takes a lot of practice to shoot well and effectively, how much more will it take to do so on an extremity, that is possibly moving and certainly smaller than where you really want to aim? Again, if you aren't familiar with handgun shooting, it would be well to give it a try and see how easy it is to hit a defenseless piece of paper at a given range, much less to do so in a hurry. Add to that a moving attacker, split second thinking and events, and your adrenaline coursing through your body, and you'll see that it's not so easy to hit something, even at what you considered to be a short distance away.
(BTW, put away the notion that the shotgun is going to eject a cone of destruction. It won't work that way!)
Were I in your shoes, I would be looking for a 32 revolver or a 32 Auto pistol. A "Star" pistol, which is a Chinese copy of the Soviet Tokarev TT33 might be an alternative, but there are issues with that, as well. Sticking with 32 S&W Long or 32 Auto means that you can actually get ammunition for your gun at exhorbitant, rather than stratospheric prices.
Again, were I in your shoes, I'd try to find the money for a really nice used Colt 32 or secondly, a Smith and Wesson 32. I'm not talking about something beat-up or even well-used, I mean something nice. If you aren't familiar with guns, you need someone to check a used gun out for you that you can trust. For instance, is it in time? Does it lock up soundly and is the lockwork reliable?
Should you want to go the pistol route, then a Colt Pocket Pistol is what you want, again in nice condition. The Ashani is a copy of the Colt Pocket Pistol. You will want it to be checked for operation, especially a reliable safety, and you should know whether ammo feeds smoothly and reliably through it. An extra magazine or two would also be nice.
Granted, you will pay a lot of money for something like this. Everyone else wants one, as well, and there's a reason for this.
If you go the IOF or Ashani route, you will need to be doubly vigilant about the operation of either one.
I'm sorry to tell you, that in your quest for personal security, most avenues have been blocked for you and there aren't many reasonable options.
And, as far as practicing, with the limitations that you face, I would be strongly considering getting an air pistol -- a good one, not some replica toy. At least you will be able to familiarize yourself with trigger control and sight picture, and you will train yourself 9or have someone train you) to shoot well. It may not be the same kind of shooting that you have in mind, but shooting is shooting, and with a limited quota of ammunition, you need to be throwing lead downrange, even if it is small. That's one thing I'd do, anyway.
https://gundigest.com/more/how-to/firea ... l-shooting
You can see that your work is cut out for you, and an air pistol can get you down the road with some of these concepts, because you can really practice them enough for your mind and body to learn something.