Let cook till the vegetables get soft, a couple of minutes. I sometimes add sage, omit the oregano and basil, or otherwise play with the ingredients. Both are optional, both are good. Thyme, Wor. sauce and Tabasco are the other sacred trinity of cajun cooking. Gumbo can be based on any number of things.
Seafood is classic, with shrimp, oysters, crab, or fish in any combination.
Chicken can also serve as a base. For health reasons I've been using turkey sausage lately. If you're gonna add chicken, you should have browned the diced chicken in the oil, then removed it before you made the roux. The seafood goes in after the stock. Back to the gumbo, now that you've added any meat you want, you should let it get warm and lightly browned in the roux mixture, then it's time to add the stock.