How much gigabytes is good for a laptop computer?

Wait a minute - that 500GB will refer only to the size of the hard disk inside the laptop.

The first thing you should focus on is budget. Expect to pay a lot you want a gaming laptop. Usually that would involve something like an I7-core and 8GB of fast RAM inside the box.

You may be forced to balance up what you want with what you can afford. Gaming laptops are not cheap. And cheap laptops won't be capable of running the very latest games (or their mods).

500s good

I recommend a desktop if you want to play games. You often get more power for the same price. But 500GB is plenty for storing modpacks. Just to come back to spare_widget's answer, it would be cheaper to buy an overclocked i5 instead if you want to get a powerful computer or even get an AMD processor.