Develop complex custom wordpress backend plugin handling gravity forms data

Looking for highly experienced developer with significant understanding of wordpress backend and gravity forms ecosystem. Our website currently comprises a detailed conditional questionnaire which generates a PDF document in response to submissions. We wish to add extra functionality for clients whereby they use the generated document to intiate a "tender" process, the document is sent out to respondents and their responses are collated and made available for comparison and processing the wordpress backend. Detailed spec attached. It may be possible to build on or fork existing open source plugins to save time and cost, for example WP Bid Manager plugin looks to provide some of the required functionality. Applicants must include evidence of successful complex wordpress plugin development, and extensive experience with gravity forms and/or gravitypdf. Price negotiable based on experience and record of previous success.