Hi Paweł,
As far as I am aware, there is not really much you could do (had exactly same questions).
You could set edit mode per workflow basis (It's not per form, as if multiple forms are going through single workflow it is set for all of the forms), no way to limit it to specific users/groups it's the same for all.
Dynamic mode is based on assigned tasks - if user have a task, then it will open the form in edit mode, else in read mode. So unless you set it to read, it will work as you have described.
You could try to recreate that 'My tasks' pane, as a dashboard - I've prepared a proof of concept which requires some more tinkering but i can't see any other option.
* https://community.webcon.com/forum/thread/3772/15