1. Archive (zip, rar, cab, etc.) files are by their nature are inert, you need to extract the files and then you have to run them to be a threat. Long before that happens avast's Standard Shield should have scanned them and before an executable is run that is scanned.
2. No the boot-time scan isn't as thorough or do everything or scan archives, it would take too long, it would also be scanning files that frankly are of little or no risk swap thorough for paranoid and you have a good example.
I have only ever done a Through Scan with Archives once shortly after installation just to ensure a clean start state after installation if you select it. I believe a boot-time scan will be quicker and reasonably effective. Like everything in life things are a compromise.
3. For me that is a Standard scan without archives, read the image extract again and that tells you what will be scanned. The Quick is another option, but personally I find the Standard sensitivity the best compromise.
4. There won't be much in memory (though I don't know for sure if it is scanned), that is another point of running it, as windows hasn't fully started. So on occasion where avast finds an infection in memory one of the option is to run a boot-time scan as it won't be in memory.