You’ve got a lot of topics in that question… 🙂
When you mention setting a task value Day = 32 hours, assigning 1 resource extends the task to 4 days, and 4 resources brings duration into 1 day, this is exactly how Project works. Your value day of 32 hours is the Work field value on the task level. If you indicate the Task Work value is 32 hours and assign 1 resource available hours per day, Project will change the task duration to 4 days.
In your second scenario, you’re asking about how to configure a task needing 500 hours of work but having only 5 days to accomplish it with resources only available 8 hours per day. To your point, you need 100 hours per day of labor, and with 8 hour per day resources, the only way that can be accomplished is with 12.5 resources assigned to the task (100/8).
Project WILL allow you to change the duration and if you do that on a Fixed Work task, project will change the resource assignment units to keep that Duration = Work / Availability formula in balance. However, it does it in a somewhat sneaky manner. Assume you had your 500 hour fixed work task with 4 resources assigned each with assignment units = 100%. Initially the task duration will be about 15+ days (500/32). If you manually change the duration to 5 days, you’ve now overridden the formula and since work is locked (fixed work), and you changed the duration, the only thing project can do to keep the formula in balance is to change the assignment units. This is the sneaky part. Project doesn’t actually change the resource assignment units values. It leaves them at 100%. What it actually does is to change the value in a field named “Peak”. Peak is the actual units required to complete the work in the duration. So the assignment units will show 100%, but the Peak field will now show a value of over 300%, meaning the resource will need to do the work of over 3 resources to accomplish the 500 hours of work in 5 days. The only way to fix this is to add additional resources until the Peak value on each assigned resource is at or below 100%.
Finally, you mention contouring the work on a task. As in 50 hours on day 1, 100 hours on days 2-4, etc. Project has a task level field named Work Contour. This field allows you to specify how project should “arrange” the work on the task. For example, in a bell curve model, front loaded, back loaded, or a flat model. There’s about 6 different contour patterns, including custom, which means you manually enter the planned work for each day. The only time this feature really works is if you have a Fixed Duration task and a small amount of work. Meaning for example, you have 5 days to complete 16 hours of work.
Some of these are rather complicated topics and hard to discuss thoroughly in a written forum such as this. If this doesn’t help, we could arrange an offline discussion if you would like.