I don't consider it rude to post a ton of images of great art such as yours!! I say flood our gallery!
As for mailing right away, in my experience people will hold a card and mail at the same time usually. I personally will mail the card right off when it is ready because that is easier for me to check it right off the list of things I need to do. just ask the person you are trading with.
For mailing. There are threads devoted to that. When I am not on my phone I will look for it to link for you I think it is one of the sticky threads.
For active times. I have been away from the site for a while so I do. It know the trends so well. There is certinqlly not as much art here as compaired to the other site. Fewer people here. But the ones that are here are all awesome.