Just picked this guy up last week. He came with a 135g, a 13+ inch pleco, and two goldfish, which he has been living with for a for a couple months. He is a really good beggar.
Here's an update after a few months. I have moved the pleco in with my jaguar cichlid and vieja synspilum. One of the goldfish is still alive, as are 4 giant danios and a few algae eaters. He mostly just chills in his cave or buries himself in the sand, but springs to life if he thinks it might be feeding time. He has grown an inch or so since the last update.
Why do you think those puffers kept dying on you? Was the brackish water difficult for you? How about weekly water changes or pre-cycling the tank before you get the puffer?
I'd get a smaller FW species to live a few years, before you attempt the giant ones. How about some dwarf puffers?