Hi,
Anything that downloads and is shown in your copy of TF will be there in offline mode. You can also pretty easily point TF to a new directory (from another computer perhaps, or on an external drive) with maps.dat files in it. Just use the map directory setting, and restart TF.
There is a batch download tool, available in the pro version. However it can only be enabled for the servers that allow it. You can download the old aerials and one of the color aerial sets.
Hope that helps,
Scott