Welcome to AA.
First off, do you have any experience in keeping sw
aquariums? If not, I'd look into getting yourself a book and reading it, because clowns cannot breed in shoddy water conditions.
There is a LOT to know about the general upkeep of a saltwater tank, not to mention the expenses. Knowing what you are getting into and the maintence required will save you a lot of time and money.
Second, it will take you atleast a year, if not 2 years, to get clowns to breed for you (in most cases). They need to be bought young, allowed to mature together and form a breeding pair (the sex change to female occuring) and then you wait for them to become old enough to breed. It took my clowns about 2 years to figure it out. They are not like freshwater fish in which most cases you just put them together and a week later you have eggs/fry.
If you are interested still, I would go with atleast a 30 gallon tank and get only 2 percula or ocellaris clownfish. They are the easiest to breed, I believe. Getting more than 2 will likely ruin your chance of breeding occuring. You will also need a smaller tank, a 10 gallon or so, to raise the eggs and fry in. Lots of food (baby brine shrimp, artemia, greenwater cultures, etc.) sponge filters, etc. All in all, it isn't easy.