To burn automatically with DVDFlick, go to Project Settings when you first start your project. Click on Burning, then put a check mark in the box that says Burn project to disc. You'll need to make sure your burner is recognized by the program (will be listed in the drop down box in that window) and you'll need to set the burning speed. DVDFlick uses ImgBurn for the actual burn, and ImgBurn is included in the download package with DVDFlick. You can also install ImgBurn separately if you prefer.
Both DVDFlick and AVStoDVD will compress the video to fit your target dvd size. Both have options to make the video fit either a DVD-5 (4.3gb) or a double layer DVD-9 which can hold 7.95gb. Most people want to use regular single layer dvds, so use the DVD-5 setting for that.
ConvertX can do all of this also.