First time i used paintbrush, i examined everything in room.
Now when i go in, i just go to the empty frame on east wall, get nice and close and examine it. So the answer is yes and no...once you've examined all the other frames, you don't have to do it again (or it may not have done anything the first time and just be a myth).
For opening the door, get up close and examine the frame on right. If you're close enough you'll get a message along the lines of "the paintbrush of souls begins to fill up the canvas". That's when you wait 30 seconds. And you'll get a message, either "you use the paintbrush of souls to project an image onto the canvas" or "you were unable to fill up the canvas". In the first case, the screen flashes white and the door opens, second case, you have to try again.
As for aggro, i've had the torama in the hallway right before the room aggro to a 70, and i think 71 or 72 is the absolute cut off for aggro in that part of the temple (not counting magic aggro from the manipulator or going through prelate key doors).
At 70, you may not get aggro, the tonberrys have to spawn as their highest possible level to get you, but as soon as that one does, all his little bug eyed friends are going to jump in.
The good news is, any party going to do ZM4 (using the sleep and pull one at a time method) should have no problem destroying 5 or 6 easy prey tonberries and a couple of tonberry elementals. Also the respawn on them is pretty long, so you'll get a few chances to attempt to open the door if you fail.
* all phrases given are paraphrased, but that's the general theme to them.
Edited, Thu Feb 23 18:07:05 2006 by Bigkillian
A bunch of 90s
Alchemy 100 + 3 + Anima Synthesis + Iatrochemistry + Tritration
Woodworking 60 + Lumberjack + Wood Ensorcelment