A single entry is 1900 and a multiple entry is 3800. You can get it the same day you get your extension is approved. It's common to get under consideration stamp for a non O marriage visa. I wouldn't be too concerned about approval, if they gave you a UC stamp.
Have pass book updated every month with foreign deposit for previous year and the month of application. You can call immigration where you will apply to be sure, but it worked for my neighbour.