......And the black stuff on the glass is just creosote, a good HOT fire will clear that up. If you are ALWAYS getting a buildup of that stuff, it could mean that you aren't having hot enough fires, and that problem should solve itself come January, if it gets cold where you are. If you burn the insert hot enough, the firebricks will be tan or grey, and the glass mostly clear.
Get the stuff now, sweep that chimney now and often, you will them have a idea on how your system is working and the tools ready to use.