Do you have any effects on any of these layers? Trapcode Particular, for example makes your .aep larger than you might expect—each instance, in fact, adds about 8 MB to your project file's size, and there's no way to reduce that.
There will always be a base data structure in an AE project file and the references to external assets are only a minor part. There's ll be a default timeline and comp definition in the file, info on the last workspace used and how windows were arranged, the state of certain non-persistent settings and options that aren't stored in the prefs and so on. Anyway, utterly irrelevant for practical purposes...
Really no effect, i just use simple expression and play opacity with the text layer.
I just noticed something. 1) I create my aep file (text layer, 2 images, expression) 2) I save the weight is negligible 150Kb 3) I imported an aep file (purchased template) which contains effects and whose weight is around 10MB. 4) I save the weight goes to 10.5MB (logical) 5) I delete the 10MB template and I save again 6) The weight goes from 10.5Mo to ... 10Mo