As much as possible, It is always strongly advised to maintain a valid status in the US based on my experience w/ immigration attorneys. However, in your case, I130 is approved & 485 is in progress, which will most likely be approved as well. It's a personal choice to whether take the 12 credit hours & continue maintaining status or stay out of college relying entirely on the 485 petition.

As for notifying the DSO, you can simply scan & email or mail them a copy of your approved I-130 & pend