Binary attachments are not supported. Although it would not be difficult to add a feature that saves the binary attachment to a directory and post a link in the forum.

There is a variable called $max_msg_length that can be set to the max number of lines that a message can be before it is assumed the post is a binary one. The default setting is 300 lines. In addition there is a spam filter to check for 'begin 644' in the body and reject the post if it is found (begin 644 means the post is binary).

As for busy groups. It all depends on your news server speed, your connection speed and the amount of space you have available for storage. But for practical use where you would maybe have 10-20 newsgroups, there will be no problem at all.