> 1) Is it easy to get rid of the checkboxes (as I am filtering the source they are always checked)? Maybe subclass and override the function?
other way around, use the parentclass ComplexTableField instead if you don't need the relation-setting through checkboxes :)
> 2) I'd like to show values from the Image class in the table somehow (e.g. filename).
you can show any properties that can be accessed on the normal object (or more with setCustomQuery())
> 3) The ImageField control seems to require that the record is added before the image can be selected. This is a pain because you have to add a PortfolioImage and then edit it to choose an image.
thats by design, nothing you can easily change without rebuilding the ImageField, as its using iframes for upload. i agree that usability could be better in this use-case...