No number. The more the better but as soon as you have one malf.... how many more to make sure it was a fluke? bad round? mag problem(good idea to number/label your mags)? worn out spring? etc
As mentioned above, being familiar with the gun and practice clearing malfunctions is going to be more important than shooting to XXXrds to call it good.
The very first thing that I do to any new or even used pistol OR revo is take it apart.
I then polish and smooth everything up. If it is a revo I push a piece of a cotton ball through the cylinders chambers and the bbl,very slowly seeing if anything grabs a piece of cotton. I also do this with pistol bbls.
This is a good "tell" of the smallest imperfections.
After that - -> I shoot. First training ammo,then finally carry or hunting ammo. I adjust sights accordingly.
How many rounds ?? Some guns 200 or so. Glocks about 100 total. This,without a single hiccup. My 42 got feelin' good pretty quick. But then I buffed the crap outta it. I also smoothed the mags feed lips. First time I have ever done this to a Glock mag. I gently do this to some MagPul's for my 5.56 and 308's.
The majic word is RELIABILITY. ---- SAWMAN
That is one of the reasons I go to the IDPA competitions. Yes it is a game, but it really showed me some flaws in my skills and in some cases equipment. I have a gun that I shot in the square range several times. I have taken it to two matches and had malfunctions both times. It can no longer be a carry gun. As mentioned above, these matches have made me more comfortable clearing malfunctions. It pisses me off when they happen in the match but fighting through it is good training. It is a fun way to put some rounds down range too.
at least 1 box of self defense hollow points. Some do two boxes and then a box of regular ammo. That should give you an idea. If it jams with that you got issues
Short answer is whatever amount is needed to achieve operator AND firearm confidence.
I don't run out and buy the "latest, greatest, hot,high demand,..." gun. I wait until a lot are in shooters hands, giving time for problems surface.
Then buy what's makes the grade. Not all pro & cons are viewed the same by all users/reviewers. So you "start" with a history of sorts and know potential issues. Normally, this would only be ammo or projectile sensitivities.* Cheaper range ammo (ball, alum case, lower vel.) IS NOT THE SAME as full power, special projectile, brass case defense ammo. That's the gun/ammo combination you need to have confidence in and proficiency (handling, reload, malfunction, day, low light) with and may be "locked in" prior to achieving operator confidence. At this point you can supplement "range ammo" for training economy.
Periodically, I will first shoot my EDC "as is/loaded", then refresh train (range ammo) then finish with my EDC spare mag. Follow with clean (mags too), lube and fresh defensive ammo.
Most things that are called "gun malfunctions"
are usually "crappy ammo malfunctions".
So with that in mind, just get something from a company with a solid rep, then test it with sufficient amounts of Reliable Ammo so that you are familiar with how it acts. Take it on a few IDPA matches, if it performs well, that's a good one!