Definitely, Creating a mock-up of your marketplace idea before diving into coding is a great approach. It allows you to visualize the layout, features, and user experience without investing too much time in coding. Plus, it can help you gather feedback early on and make necessary adjustments before starting the development process. Mock-ups can be a valuable tool in the planning and design phase of your project.

Raising capital, whether or not it involves federal opportunity zone tax credits, is a complex process with several challenging aspects:
1. Convincing investors.
2. Regulatory and compliance issues.
3. Access to networks.
4. Competition for funds.
5. Understanding and leveraging tax incentives.
6. Valuation disagreement.
Overall, the most challenging part of raising capital lies in a combination of demonstrating viability, navigating legal and regulatory landscapes, building investor relationships, standing out in a competitive market, effectively using tax incentives, and aligning on valuation and investment terms.