Smaller puffers and porcupines are bad decisions with lions, dogfaces may be hit or miss. In a 90 with those 2 large fish, the chances of them confronting each other is much higher.
A tusk would get the same size it would in any other tank, about 9" or so, but that's years, they'll get 7" in about 2 years. A 90 will hold a smaller one for more or less a year, depending on purchase size. A tiny Indo Harlequin (2.5" is the smallest I'd buy) would be fine for much longer in there.