Project Overview in Project Details

You can use fusion to fill in that information from the data on the custom form.  If it's just one portfolio/project sponsor, you could create a template for it.

If you go to setup > interface > layout templates > choose the layout template > on the left side under "Customize what users see" choose Project > The overview section is listed on the right. You can uncheck some of those fields that you do not wat to see.

As Tracy say the fields and position are selectable from the layout template, We have a custom form attached to ours so i positioned this above the overview as my team prefer to go direct to the Custom form information

I'm not sure if I read that correctly, but for me it sounds like you may want to edit layout template. There you can specify which out-of-the box WF fields are visible in Project Details. If you hide all fields from a given section, section is no longer visible.
e.g. in our instance all fields related to "Project stakeholders" are disabled:

so effectively, users assigned to this layout template don't see this section when looking up Project Details

Adding on to this question, is there a way to have the custom form section be open upon entering instead of being collapsed every time?