1. It is generally a good practice to purchase the largest aquarium that you can actually afford. A larger aquarium will be less susceptible to quick changes in the chemistry, and will offer much more stability.
2. Angelfish are normally very peaceful fish, in times of breeding they can get aggressive. It is a good idea to only keep one pair of mating angelfish in the same aquarium, as more of them can lead to infighting.
3. Do not overfeed the fish in your aquarium. Keep your feeding times at scheduled intervals to avoid overfeeding. If you are just starting your feeding routine, start out small and increase the amounts you put in on how much your fish eat.