Yes, you can do everything in one file. I set mine to make a new file each day starting at midnight, usually taking one image every 4 seconds, which provides a fairly fluid image flow, specially with cloud formations. During storms I may change that to every 2 seconds, which slows down the storms a bit. As far as HD quality, I'm not sure on that, I think EvoCam is certainly capable of it. Mostly it depends on the camera and it's driver, specially if you are direct connected. My system takes the image from a standard composite video feed coming off a video relay transmitter that I use to keep cables from running through the house and to keep my wife from strangling me with it
I think you can still try EvoCam for like 30 days and see if you like it. Their support people over there are pretty good about helping with new cameras too, if they don't currently support one, they can work with you (it's been a while, they did work with me a few times).
Hope that helps a little.
Doc
ps, if you look at my camera at present, you may see images from several different cameras, a night sky 360? camera, and an all day camera in wide angle set to the northern sky 24/7. Unfortunately, I loose a bit of focus due to the transmitter relay, I've been working on that for over a year now. It's a major pain.