Yeah, precisely! I knew it was way off when my friend and I were talking about just going with 480x800 standard canvass.
So I guess we need to scale it down a bit, yes and have an engine that just stretches it out, yes?
About vector graphics; I saw this one guy make a tutorial about adaptive pixel art by laying them down on grids in illustrator and making them seem like pixel art. Thus pseudo-pixel. I dunno how effective that is though but I cant afford illusrator so I'm fine with my free software.
1) I think the ideal way to do multiple resolutions is to have a game where aspect ratio doesn't matter and the camera just shows wider/narrower area if your screen has bigger/smaller resolution. But that is not possible with all kinds of games.
2) The next option is to lock the aspect ratio and block the rest out with black bars if the end device aspect ratio doesn't match. Game camera pixel size will then be scaled according to the device screen pixel size as well. In this case for the graphic content you usually pick the largest resolution available so you don't have to scale up your images which always results in loss of quality.
If you want traditional "accurate" pixel art and go for 2) then I don't recommend using raster images. Pixel art needs to be sharp and scaling them up or down always results in blurring due to resampling and your art is basically just not the same anymore as pixels get recalculated. You could perhaps also make dedicated pixel art assets for each of the resolutions if that makes sense for you and for your game project.
But the tutorial you mention about adaptive pixel art could be a fair solution. A program called Inkscape can probably do it as well and is free to use, so I recommend trying it out.