the resource calendar did not show up in the gantt chart but it shows
at the resource usage sheet
The green shading on the Gantt chart is based only on the Project Calendar* and is for display only. However, Microsoft Project does take into account the Resources' base calendars and Task calendars (if used) when scheduling tasks (e.g. determining the start ...
Although it has been pointed out that this type of planning will not be effective, there is a way to distribute work based on percentage of time in Project.
Click on the task and then click on the Details view on the ribbon (Task -> Properties -> Details).
In the detail view, change your task type to "Fixed Duration".
Then add your resource and modify ...
Yes. On task 100 you would add both task 20 and task 30 as predecessors, with a finish-to-start relationship and 20 days (4 weeks) of lag. Once added, the earliest task 100 will start is 4 weeks after the latest finish of tasks 20 and 30.