This document is the technical elaboration milestone for FAIMS3 development. For more details on FAIMS3 see https://osf.io/mqk45/. In December 2019 the Australian Research Data Commons (ARDC) awarded a team of researchers led by Macquarie University $600,000 over three years to build a digital platform for data collection in the field and offline. This was matched by $720,920 in co-investment from project partners. FAIMS3 is a ground-up rewrite of the FAIMS Mobile (v2.6) offline-capable, geospatial, multimedia, field-data collection application. This rewrite is designed to be multi-platform, maintainable, and to support data collection at a citizen-science scale. The code and platform should last for at least five years, assuming regular maintenance. This document proposes how we can achieve these objectives.