Interpolate Effects in After Effects
Yes, do it as one effect and use the graph editor to use a non-linear curve.  You can alter the curve to respond however you'd like then.



Simply click on the graph looking icon next to your parameter that you are keying on so that it will appear in the graph editor.  Then open the graph editor (icon closest to the timeline on the top (looks like a graph).  Select an option such as Auto Bezier or Auto Ease In or Auto Ease Out as you desire.  Auto Bezier will give you more control over how the curve responds by dragging the bezier anchors (the ones that appear off to the side of the end points.)

Also, don't use a transition effect, use a scale with keyframes.