There's been a lot of good info here so far, but, If I may, I'll add an idea or two from practical experience.
After you have developed good basic proficiency with a handgun, get a copy of Ed McGivern's book 'Fast and Fancy Pistol and Revolver Shooting' (that title may not be exactly right, but its close)
Note, especially, the demonstrations of firing with reasonable accuracy and great rapidity from inconvenient or uncomfortable positions.
If you are ever so unfortunate as to need to rely on a handgun to save your life (or that of a friend, family member, etc.), literally fractions of a second's time may make all the difference, and you may not be able to get into a stable position.
Learning, training, and practicing firing a handgun with one hand, (you may only have the use of one hand, for any number of reasons), and from various unusual and uncomfortable positions, may be the 'edge' which could literally make the difference between life and death.
Imagine, for example, having been knocked to the ground, feeling a bit 'stunned', and your 'strong hand' disabled. Being able to deploy your weapon with your 'weak hand', quickly, and fire with reasonable accuracy may be your means of survival.
Many years ago, I had the opportunity to go through some basic training provided by a couple of men who had been combat veterans in a 'special forces' grade of military unit.
I have to admit that I got to hear 'too slow, you're dead', or 'too sloppy, you just killed a friendly before the enemy killed you' and similar things, quite a few times.
One of their training procedures was a bit challenging......but it does give you some idea of what a real confrontation could be like.
In this one, they put a sack over my head, spun me around, and pushed me back and forth between them til I was stumbling, whilst shouting obscenities and contradictory information in my ears.
When they thought that they had me sufficiently disoriented, and 'off-balance', they pulled the sack off my head, revealing two dummies, a 'friendly' and an 'enemy'.
I was expected to draw a pistol (cond 1) and engage the enemy (and the difference in appearance between the enemy and the friendly was subtle enough that it required a close look) in two seconds or less.
To 'make it interesting', just as the sack was pulled off my head, and I saw the dummies, one of the men kicked my legs out from under me, to one side, so that I'd fall sideways, whilst evaluating the friendly from the enemy, and engaging the enemy.
'Too slow, you are dead'
Well, the truth is that I learned that I 'don't have what it takes' to be a gun-fighter......so thats why I call myself a 'non-violent pacifist'.
(but training the best you are able with a handgun gives you the best opportunity to maintain the position of a 'non-violent pacifist', cos then you'll know what to do if bad circumstances won't allow you to remain purely 'non-violent')