I'm not entirely certain of this as a fact with many different laptops, OSes, memory management software and system setups it may be possible to tweak system memory use. If your not using anything and the laptop is generally on a default setup then I believe that this is a reasonable assumption.
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I don't believe it does, but it rather depends on what laptop and graphics 'card' you have.
If you have a graphics chip on board (built into the motherboard) that doesn't generally have any of its own memory, they generally have a sum of the mail memory 'allocated' for the graphics chip. So I wouldn't expect any of that allocated graphics memory to be used (as this is controlled by the OS), but I believe it is possible for the graphics to use more than that allocated if it is available.
Avast's memory use I believe would be governed by the OS as well in the same way as other applications/services, etc. so it would be restricted in what it can use.
If your laptop has a dedicated graphics 'card' that would have onboard memory which under normal circumstances would not be used for anything other than graphics use.
