"Do you still make money from microstock?"

Yes, but less than I used to

"I'm making like $70 without uploading anything and I have 500 images. What time and how many images do you think I need to make $500, for example?"

Impossible to say, but a lot more than 3571. Extrapolation never works here.

"How do you upload your content to every agency at the same time?"

IPTC and FTP help a lot. Some even use special services. But most are aimed at photos, not illustrations.

I make money from microstock, actually, for me my monthly and yearly income is still increasing altogether.

How many one needs to make a specific sum, it depends on many things. First thing to do is to test some new vectors, try new topics, etc. and after a while you will see which could work for you. I usually make like 10 vectors when I am testing a new style/topic, and check how they are performing after a while, 1-2 months later. If they sell, I get into it, if not, I try something new again.
Check out the trends, look at the market, research what is selling (sorting searches by Popular, for example) and do something that is in demand.
Quality is also important, but is very subjective. The main indicator of the performance is commercial value - demand, applicability, etc.
FYI, in my own case, I was making 500$/month with ~700 vectors.

You can also upload to many agencies, but from my experience only some bigger ones are worth it, especially bothering with at first: Adobestock, GettyImages, Shutterstock. If you can make money with these, you might make some with the little ones too, if not, might be just a waste of time and effort.

If you want to give it a chance, do not expect sudden increase. It is an investment that takes time, I would say 3 months at least. Make some new illustration, be consistent, upload every week, persevere and after 3 months draw a conclusion: is your income progressing enough for you to continue?

There's no easy answer, but good luck to you!