Yeah you would need to upgrade eventually for a group of 4A breeding pair of the smaller type of bass would do great in a tank that size.
how many could peacock bass could i havein therethats a huge tank for a single peacock bass, a tank of that size can easily accommodate a few more fish, is there a specific reason as why u would like to only keep one? budget? worried of fights?
i feel that it would be underutilized ur tank, but thats up to you, perhasp u can add in other fish ?