Mike is right, you cannot change some attributes on the fly, but "easy" stuff like framerate, brightness, gain, and other "easy" stuff that is supported by your cam is possible.
Regarding 1: It depends on your application. I have an application were I just save the images in RAM (in array of images) and save them afterwards file by file in a folder. You can later display the files like a movie inside your vi or export it in a converted and compressed avi. File names for the images could be ordinary increment or e.g. millisec value when shoot was done.
markus