1.Could there be growth in heaven?
I believe so.
Growth does not necessarily imply that anything is (grievously) lacking in the saved soul. That is to say, if a soul enjoys the beatific vision, it lacks nothing of what it ought to have; but this does not mean that it cannot grow even holier, even closer to God. Some might say that this logically implies that some souls are "worse off" than others, and this would imply that there is evil in heaven. But in the equation of the Union between the Infinite and the finite, the finite are by definition infinitely "lacking"--yet it is a "lacking" which is itself glorified, for Christ himself glorifies finitude. The difference between the infinite God and the finite saints glorifies God, so also does the continual--infinite!--progress of the Heavenly Liturgy toward God glorify God. Thus I believe that Heaven is not a static, but is rather a "progressive" place.
2. On drawing lines.
The intellect cannot but help to draw lines, to distinguish, and this is no less true in the domain of human action. The moral line is neither wholly straight nor is it fuzzy or indeterminate. Beginning with the law of God and progressing through considerations of virtues, circumstances, and codifications, we find that the justice or injustice of "lines" has nothing to do with whether a line is "man-made" (for such "lines," as are found in canon and civil law, are prudentially necessary, even if they are sometimes artificially strict) or whether a line withholds reaction to an imperfect behavior (for human beings are often unready for, and would be harmed by, immediately imposed perfection). The justice of a "rule" lies solely and simply in whether it can be demonstrated, within its prudential context, to serve human dignity in its immediate state and ultimate goal.