Hi Marco,
I've had no time to look into this, but here are some answers:
Problem 1: You're right, the name was wrong, my older version of content was called 'content' instead of 'learning-content', I've fixed it in the cvs, I have not tested this though.
Problem 2: It must be the task_item_id, you should set it in the task-view.tcl using the task_id, I need to update the patch to fix this, will do it later.
Problem 3: Probably something changed in the most recent versions of xowiki, I have not tested the Planner with xowiki 0.118, the required version is 0.106.1, the one in the oacs-5-4 branch, I suggest you use that version for now.
Problem 4 and 5: will look into it later :)
Hope this helps,