In terms of a modern resident antivirus I would say it isn't unusual.
The way avast works it will fluctuate in size as it periodically carries out its own house keeping. So I wouldn't recommend trying to delete anything, the fact that you may well bump into the avast self-defence module.
My current size is 351MB, when you consider that just the virus definitions runs at around 126MB unpacked (this will also grow) and at any time
Hard drive space now on a modern system 350MB is a drop in the ocean, if it isn't then you are getting to the point where you would need to upgrade your hard drive. Any less than 15% free space windows has a fit and won't even do a defrag, certainly that will cause performance issues if the drive is fragmented.
The aswAR1.log can get a bit large (nothing much on my system 2,552KB), but deleting it will achieve nothing as it is the anti-rootkit scan log and the next time it is run that log is likely to be recreated, it is overwritten and not a cumulative log.
