I was trying to test a promotion on 4.3 Beta2 for a gallery image (Our Picks)

I realised that ;

• The picture is not automatically added to image selections
• The title of the promotion can not be changed ( directly getting text from Caption)

Shouldnt these both be available ?

May be a bug. You can report that:

https://invisioncommunity.com/4bugtrack/alpha-and-beta-reports/

First issue I'll take care of (but yes, the bug tracker is a better choice in the future).

Second issue doesn't look to be an actual issue.