I would recommend that you explore this question by doing a Proof of Concept (POC), starting with one of the simpler forms, recreating it with Form Builder, and migrating your existing data to the new format. This should help you get a feel for how well Orbeon Forms' capabilities match your needs, and how much work is involved in migrating all of your forms and data.
Would such an approach work for you? If so, we can help your team with a Dev Support package (
https://www.orbeon.com/services).
-Alex