I have about a dozen AR500 gongs from 2" up to 12", plus one 2/3 scale human silhouette. They have seen upwards of 100k rounds and are still smooth on the front.
3/4" pipe will last a long time. I doubt if splatter will hurt it.
I used smaller chain with most of mine. I found some old chain link fence posts. I cut the post into 12" or so pieces and slid the chain thru it as a shield. The post will take a direct hit from a .44 mag and usually just dents. I just have mine hung from a wooden frame. I put angle iron on the edge of the frame to protect it from splatter.
I got most of mine from Magnum Steel. They have good prices plus free shipping. In addition to gongs, I have bought silhouettes from them. They are very nice for the price.
I shoot a lot of mild 185 gr SWC .45 at my gongs. They are just under 800 fps. The bullet flattens out in a nice little button about the size of a nickel.