Hi Cyril
Thanks for the XML. I created a page with it and i can see what you are trying to achieve.
I think it would be better to create a popup for the create a new task or event. This way you can create a model action that when the record is created it uses the {{$Param.id}} to update the related opportunity id to the task or event. This way you will present the user with a consistent Ui as opposed to switching between Salesforce and Skuid Ui. Also I noticed that you have more than 1 save button on your page. The best practice is to use 1 save button on the page and set it to listen for all the models that will be updtaed in your page.
Hope this helps.
