1. You should never used any alcohol to clean the inside of your aquarium. Alcohol can pose health problems for the fish in your aquarium.
2. 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.
3. 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.