Can I force finder to open without loading previous files?
Try deleting the savedState directory:

rm -r ~/Library/Saved\ Application\ State/com.apple.finder.savedState/


When I tried running killall -kill Finder, that worked, but open -Fa Finder or command-clicking Finder's Dock icon didn't.

You could also try to:


Disable ~/Library/Preferences/com.apple.Finder.plist by temporarily moving it somewhere else.
Cause a kernel panic with sudo dtrace -w -n 'BEGIN{panic();}'. There is normally an option to disable restoring state after kernel panics.
Temporarily unload the launchd agent with launchctl unload /System/Library/LaunchAgents/com.apple.Finder.plist. There is normally a dialog about restoring state after crashes, but maybe it's not shown if the program is opened by launchd.