I was considering getting a fahaka for a long time a few months ago, but just put off setting up the tank and never got around to it. Fahaka puffers need a 120g minimum with a lot of filtration. They produce a lot of waste and are messy eaters. I would personally just put the fahaka in the tank its going to live in for life. Because it would be a pita trying to move a 12" puffer out of a 90g that can't be exposed to air.
Here is a good basic page with information on them...http://www.**************.com/forum/ug.php/v/PufferPedia/Freshwater/T_Lineatus/
The members the are rude though and think they're always right because they're self-proclaimed experts... at least in my experience there...