.
'Knowing what I know now' in relation to a few years ago I would say one of the most important specs on a milling machine is the distance from 'Spindle to bed'
This being due to once say an ER type collet holder and a decent vice has been added the available working space can be reduced considerably from what you thought you had available. – Start adding a rotary table with a chuck mounted on it and the distance is reduced even more.
This may or may not be an issue depending upon what you intend to machine upon the mill. But I would say one always needs more capacity than one 'initially thinks' they do.
Nick