To minimize a Wonder's drain on your citys production time, you should maintain a well-connected network of smaller cities surrounding your SSC nexus and build caravans. These caravans should not be employed for trade - it wouldn't be preferable as all of your trade routes should run overseas - but rather as means to expedite Wonder production.
Since you have discovered Trade entailed by Banking and ultimately Democracy, you can mete out the SSC's production between any number of cities using Caravans. A Caravan/Freight, its home city, cargo and rank notwithstanding, will invariably add 50 shields the cost of the unit itself - to any Wonder production. The Colossus, which is essential to any SSC, requires a mere 200 shields, or 4 Caravans; since Caravan induction can take place all in one turn, even the cheating AI civilizations will not keep up. Autonomous production is not a key element to a SSC, though improvements, mainly the Library, University and Superhighways, are necessary to build.
By reducing the Wonder production time you can focus on building "happiness" improvements. Rush to Trade and, if feasible, get both the Colossus and Hanging Gardens in your SSC; the latter adds three happy citizens and the former, of course, is a trade-boost conducive to high science. You can cumulatively increase your science production by an additional 150% with the Copernicus Observatory and Isaac Newton's College.
To maintain your SSC's food production without causing disorder, order settlers with other home cities to improve nearby terrain. With Michelangelo's Chapel and J.S. Bach's Cathedral, your SSC can grow beyond 24 (when the city can no longer work on more tiles) and you can convert additional citizens - forced to be specialists - into scientists. In addition, you can safely become a Democracy, a volatile gov't that does have its advantages.
Towards the end, the Hoover Dam will allow cheap, instant production and the SETI Program will double your research in every city.
PS: Ignore the Pyramids and the Great Library (Marco Polo's Embassy can be helpful if you are engaged in early conquest, esp. overseas, or are willing to trade advances). They have little to do with - and are often times detrimental to - the SSC strategy.