OK. I will _try_ to help here. I am not an expert, but I am struggling through just what you are, only I have got through most of the basics. I am only using Studio. I hope the settings I give are of use.
The Project Properties are (mostly..more on that later 🙂 ) not what matter when you render. They are to do with preview and editing as much as anything.
I will assume you are saving to disc. As far as I have seen it’s by far the best way to go about it, even if you want a DVD. I have not tried the Youtube one, but AFAICS these are just automated versions of ones you can do, and may not be the best.
When you render, you need to set the video output size to what the chosen _renderer_ “template” does. So you need to move down the Render As window until you see Customise Template. In there you will start to go mad……but you will see choices about the Frame Height and Width. What choices you have on many of these settings depends on which template you choose. That will be enforced by what you want the output to be used for, and whether you get satisfactory output quality from that Template.
It can be really messy working out what works for you, but in the end you will settle for one or two….however
Now, having set the height and width, you will _still_ find that when you play the rendered output, in most cases you will see a “letterboxed” play, with it not filling the entire playback window. Here you need to go even further down the Render As DBox and ask to Stretch Video to Fill the output frame size (do not letterbox). I am not sure of the mechanics her: I would have through the player would take care of that, but anyhow….
Having said all of that I have just found that if you set the Project Properties to an aspect ratio that does not match your input video, you get a funny AR on the output, no matter what you set in the Template.
Hope that helps
Nick