Can you mix gouramis, Angelfish, and Cichlids at different times.?

I am planning on getting a 75 gallon Cichlid aquarium, the problem is I want some variety. i already know all the fish that I am getting can go together but can they go in at different times? Fish list: Plecostomus Tiger Oscar Cichlid Black Convict Cichlid Firemouth Cichlid 4 Veiled angelfish (one will be a... show more I am planning on getting a 75 gallon Cichlid aquarium, the problem is I want some variety. i already know all the fish that I am getting can go together but can they go in at different times?

Fish list:
Plecostomus
Tiger Oscar Cichlid
Black Convict Cichlid
Firemouth Cichlid
4 Veiled angelfish (one will be a silver veiled angel but i dont know the other 3)
Blue Gourami
Gold Gourami

(Im not planning on breeding them)
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