Hi and welcome to the Fish Forum. My advice to you would be to start with as large a saltwater tank as you can afford. It may be counter intuitive, but this can make maintaining it easier. The less water you have in a tank, the easier it is for fluctuations in water quality to affect your fish. Very small tanks don't leave much margin for error, especially with more sensitive species. We started with a 55 gallon tank ourselves for our saltwater fish only tank. It is small enough to be manageable, yet large enough for us to keep some interesting species like our favorite stars and stripes puffer fish. I have to run at the moment, but I'm sure other members can help tell you what you need to get started. What is your budget and what kind of saltwater fish are you looking to keep? Have you kept fish before?