Welcome!
The [Art] tag is simply to differentiate the different types of creative endeavors going on in the Atelier; it's recommended you use it, if only to make it easier for everyone else to find your work. Don't hotlink, though; if you want your pictures on the page here, reupload them to a site like Imgur.
We do not provide or discuss pirating games, but some of our users have contributed to or created ROMhacks of their own, so there should be no problem there. If it's working on the hack itself, it would likely go on the
Touhou Projects board. Providing a link to the hack itself would be allowed, but not to the base ROM, nor a patched one.
The IRC channels have various levels of activity depending on who's around at any time. There aren't any real rules besides the obvious - don't spam, don't be a jerk, etc.
Hope that helped. Enjoy your time here!