1. When adding new species to your aquarium, you have to ease them in. Adding too many fish too quickly can cause the ammonia and chemical levels to raise quickly. Adding fish slowly gives your filter time to catch up.
2. It is never a good idea to hand freed a Lionfish. No matter how tame you think your Lionfish to be, they still have very venomous spines and should never be hand fed.
3. 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.