Wanna go from undyed black to a silver/grey

I reckon you will have to bleach you hair 3 times to get there. First time will end up orange. The regrowth will be terrible.  Personally I would go to a salon to get this colour as you will not get a good result at home as your hair is so dark.

Bring Mexican wouldn't make too much of a difference. It's about how much pigment you have in your hair. If you have a lot of red (it looks like you probably do) it's harder, but not impossible. I know some Asian people who bleach their hair, they range from the easy to bleach to the "never get past the red stage" and white people who have very ashy brown hair (like me) who sail past the red stage but get stuck at the yellow stage, others who get struggle to get past the red stage and others who have no issues at all. There's some general things like Asian and black hair can usual take a little more abuse as it tends to be a bit coarser, but it's also far more individual.

So what I'm saying is, it doesn't matter all that much who is doing the bleaching, it's all similar, but it's also entirely individual.

The best way is to do a strand test to see how long it takes your hair to get to the desired shade.

I personally wouldn't suggest going to the salon to do it, they tend to rush it too much.

As a fellow Mexican with very dark hair, I can tell you that I can get my hair to a pale yellow( light enough to tone white/grey/silver)in one bleach. However, having used manic panic bleach kits when I first started dying, that bleach only got me to a golden yellow.
I would suggest you do either bleach baths, or two full bleaches four to six weeks apart.
Otherwise, if you can find somewhere that sells bleach, I find that purple bleach really makes a difference and gets me past the orange stage much quicker even with 20vol peroxide. I usually bleach for 30 -40 minutes to get the pale yellow for toning.