Well, you will eventually need to upgrade anyways because the lima will grow quite large quite fast. You'll be looking to upgrade to something at least 18" wide, 2' wide is better, because the lima will not only reach at least 15" (some contest 18-24") in length, but will need the extra space for its feelers.
And the royal, although it grows slow, hits at least 18" and will contribute a lot to the bioload.
If you aren't looking to upgrade (which would eventually be very detrimental to your fishes health) then i would not add anymore fish. As a growout tank, you could add a couple other fish depending on what you'll be putting them in in the end and compatibility