Legally-Binding Smart Contracts. Docusign + crypto payments + mediation services.
I consider gradient backgrounds as an option but not too sure about it. Otherwise, simple white background with black fonts and some attention-grabbing elements in bright colors. Gradient backgrounds do not require illustrations but if we go with the white background design it would need some form of illustrations. The CTA button has to always be in the top right corner, highly visible.

There's nothing specific to avoid however, I would not like the design to look like a legal agency or a realtor around the block type of website.