Hi there,

To many pictures. I need to decrease to lets say 20 Photos

Currently, it is not possibles for you to achieved that. But it would be best if you can submit a feature request regarding this issues by creating a new ticket on the forums and set it to "Feature Request", so everyone else could vote for it, the more people request on this, and we will priority consider it.

I have increased video upload to 200 MB. I changed also php.ini . It seems video upload takes endless time, nothing happened. It worked before fine with lower upload size setting.

It is based on your server itself. if you upload much bigger size, it will took much longer time to be uploaded and converted to 720p. Maybe you can consult with them and see how it goes

3. If I change just a regular article site in Joomla Admin - it will be always displayed in activity stream. Can I disable this?

By doing this http://take.ms/zF9kL any updated article(Joomla's article) will not shown on your stream. Please give it a check and see how it goes