1. Yes it is possible to download avast, just don't use the Cnet download link.
Download the latest version of avast
http://www.avast.com/eng/download-avast-home.html and save it to your HDD, somewhere you can find it again. Use that when you reinstall. Ensure that you scroll down and select the avast direct download link for the English version and not Cnet as that is for an on-line installation (not what you want to do). - Direct download for avast Home, English version,
http://files.avast.com/iavs4pro/setupeng.exe.
2. I have no idea what you mean by this "cancel out the update download for "Avast 4.8"." All you should do is download the avast setup file (37MB), go off-line, uninstall Kaspersky, reboot and then install avast.
avast should be reasonably up to date with possibly only a small incremental update on the virus signatures, but this shouldn't be large and can be don after installation.
3. What you can't do is have two resident AVs installed at the same time, even if one is disabled, low level drivers will still be running and can cause conflicts.
4. I really don't know what you are trying to achieve here, install avast or find a way to update kaspersky ?