Hi Carlton,
Are you speaking about the size of the project file or the one of the EPUB3?

The size of the project file grows together with the contents and assets that you import, so you can reduce its size by preprocessing image files or compressing video files.

As for the output file, PubCoder automatically optimizes the image objects that you insert into your layout, exporting only the required pixels. For example, if you place a 40 megepixels into a 1000x1000px image object, PubCoder will actually export a 1 megapixel image, so the file size is already optimized.
Actually, you can control the pixels density in the Project's General Settings, to support 2x (Retina) or even 3x (Retina HD) screens at the optimal quality: using the same example as before, with these settings Pubcoder will respectively export a 2000x2000px or a 3000x3000px image in the 1000x1000px image object.
You will now understand that lowering the Pixels Density is a way to quickly lower the EPUB file size.

Instead, assets included with other objects types, such as Image Gallery, Video and Audio, are just copied from your project file to your output file, so you may need to preprocess them manually to lower the output size.

As for the maximum EPUB size, I'm not aware of any limits for supported file size in the format itself.
By the way, some digital stores may define file size limits: you should be fine with a file ≤2GB on the iBooks Store.

Hello Carlton,
if you would like to publish your App into Google Play Store you should export your app for Google Play in this way:

1. follow what described here: http://docs.pubcoder.com/en/export-an-android-app/
2. when you click on Publish, select "Google Play Store Distribution", if it is not available you should fill your project setting with the correct Google Play Public key.

Differently from "Ad Hoc Distribution", if apk size would be more then 50Mb, an expansion file will be created along with the app apk.
Best regards,
Giancarlo.