Leonie's remarks are spot-on. In case they haven't glowed yet, this may help: you don't store share-able digital image files in Aperture; you create and store the _potential_ to make share-able digital image files. That's what your adjusted Versions are: instructions to make -- when needed -- a share-able digital image file. (This workflow has enormous advantages.) The parameters you can't find _within_ Aperture's adjustments (viz.: size, pixel dimensions, document size, resolution) are _file_ parameters. You select and apply them when you convert the potential stored in Aperture into an actual share-able digital image file. That process is called, in Aperture, "exporting". "Export" = makes me a share-able digital image file of this Version with these specified _file_ parameters. You specify the file parameters via an Export Preset.
There is a parlous moat to cross on the way to Aperture-vana. You must move beyond the deeply-entrenched _file-centered_ digital world, into a less object-oriented (it seems to me) distributed-data digital world. With Aperture, that means accepting -- and working with -- the _Image-centered_ model at its core.
I don't know if Aperture is a good tool for you. I do know that you will never work well with it as long as you force it to follow the channels carved out by years of file-centered habits.