Going by the comparison with your plastic pebbles, they are still young, sub-adult size. Basically "teenagers", and probably not mature yet. Most people buy about 5-6 angelfishes, and let them pair off as they grow up. The thing is, your tank may not be big enough for such a group size.
The plant in your pictures, a Syngonium species, is not suitable as an aquatic plant. They are good as plant filters for a pond system, or in a paludarium, but not as a fully aquatic plant. If that is a plastic plant then it's alright.
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