Exactly which version of InDesign are you running? You should be at InDesign CC 2015.2 to see all of Publish Online features and to handle many bug fixes. It sounds like you are not updated to the latest version.
I have InDesign CC 2015.2, I just did my update a few days ago
Thanks for reporting the issue, we already know some of them already. Please read the following status/workarounds that may help you:
1. Emailto when applied as button action will not work, is known to us... as a work around you can try creating a email hyperlink using Window->Interactive->hyperlink... New hyperlink.
2. This "click to go to URL" issue is specific to firefox and the Safari, you shall be seeing it working on chrome. To make it work on Safari and firefox, you can remove the click state of the button from button panel.
3. Since the spread has animation applied, the blending mode is dropped, this is known issue.
4. The pdf that is downloaded is a Print version, hence interactivity shall not be present, we are allowing only the print version of the document for download purposes.
I will escalate the issues you have reported for investigation.
There is no limit on the number of publications, that you can have and as of now, there is no provision to upload the published document to your own server.