Yes, should be fine in a 90 gallon for life because they top out at about 12 inches and a 90 is 18 inches deep I believe.
Tank mates are also possible as long as they are not to small to eat or the pike is not much smaller then it's tank mates. If you start with a few Juvi's, maybe something in the Parachromis sp to to with your pike, some bottom feeders, like catfish and get a few dithers, should work. The pike will not kill everything in the tank and you may have to consider that other fish may bully the pike if they are much larger. I find that although cichlids are aggressive, pikes don't seem to mind their larger relatives if they are shaped differently then they are because they don't see them as competition for food, and it seems to work both ways with the other aggressive fish not looking at pikes aggressively. But, as always, different fish have different attitudes