Is it good for gaming?
Possibly, it depends on the game and the settings you want to play at.
How much can I overclock it?
How long is a piece of string? Unfortunately, overclocking isn't an exact science, there are too many variables at work to give you a definitive answer.
The AMD A series are APUs, which in layman's terms means that the CPU and the graphics card are on the same piece of hardware. If you have a small form factor PC or don't require a lot of graphical power, this can work well.
The downside is that because resource allocation is split between two components, overall performance can be a compromise. This can be particularly true for gaming, which is one of the most demanding tasks a PC can do.