I concur with other members. I'll just add something not mentioned yet, and that is the problem that often occurs if new angelfish are added to an existing group.
When a group of angels become settled in any aquarium, that space is "theirs" to own. Within the group there is usually a pecking order, a dominant male and the subordinate fish (other males and females). As soon as a newcomer is added, he/she is seen as invading the existing angel's space. Sometimes the intruder is tolerated and even accepted, but this is frankly rare; most often it will be pursued vigorously until it is killed. In the wild, the intruder would simply swim somewhere else out of sight and smell. This is not possible in the confines of even the largest aquarium, unless it is in the thousands of gallons as in a public aquarium.
So, be happy with the 4 existing angels, and be thankful if they are getting along; this is never a certainty either.
I would add other fish though, as tankmates. The shark makes substrate fish impossible, and I would even go so far as to consider removing it. Upper fish are sometimes suddenly targeted by this species, even if all seems fine for a few months. And when he/she gets to be 6 inches, it will be a force to be reckoned with. Removing it now would allow you more options. A group of one or more species of cory, or a Whiptail catfish, or a pleco (one of the small species).
Lemon tetra at 11 is fine. Another similar shoaling fish could be added, some of the species in the Rosy clade of Hyphessobrycon are suitable (some are certainly not, so select carefully). The Roberts Tetra and Rosy Tetra are two I always suggest because with their beautiful deep burgundy/red colouration they are a nice contrast to the black/white of angels. The medium rasbora also work. Avoid any small or torpedo-shaped fish as these will likely end up being lunch; neons and cardinals for instance are not good with angelfish.