There are varying levels of success doing this, the success i have seen is introducing a group of 5 to 7 at the same time as a harem. This typically results in 1 pair and a group of subordinate fish. The success stories however are few and far between. Ive heard so many that over the course of time end up with just a pair...
It usually goes better with tank bred ones. But yes the smaller types of clowns usually won't defend more than 3-4ft of space and your tank I assume is 6 ft long. Just so none are maroon, tomato, or clarkii as those large types could claim the whole 6 ft as home.
It boils down to the individual personalities of the clownfish. Most people don't recommend adding more than a pair because the results are unpredictable.
If you're willing to give it a shot, just be prepared to remove one pair.
Most people have a 2-4ft tank. In a 6 to 8 ft tank the stocking rules change. Just like if you have a 30ft x5ft x3 ft tank you could probably add 6 small pairs. While their personality will effect how much territory they claim their species usually determines the range of how much territory they might choose to defend.