Thank you, this is a very nice requirement specification. A simple module could be implemented with a couple of days of work for an experienced Slicer developer; or in a few weeks for a newcomer with some Python programming experience. I can help with advice and maybe some work, but things would go faster if you could find someone who could help with the development. Do you know someone (a student, staff engineer, …) who could volunteer for this? Or do you have budget to hire a Slicer developer (see a few potential companies here)? You could team up and share the cost with a couple of other vascular surgery groups who would be interested in having a free, open-source, customizable EVAR planning tool.
You could also try to apply for some small internal research grant at your institution to get funding for this. The unique value proposition would not be that this tool is free but it would be more advanced, more customizable than existing commercial solutions (could support new techniques, devices, etc.).