I've been involved in various public labs for over 20 years and tried to pull together experiences and analysis in this piece, which also addresses the common dilemmas people working in labs face. I wrote it for a big gathering we hosted with dozens of labs from around the world. It's a few years old but I'm not sure it would be very different today. https://media.nesta.org.uk/documents/social_and_public_labs_-_and_the_radicals_dilemma.pdf

In my work for the government as a technical expert in a specific field, I had to provide an objective assessment on certain issues based on engineering expertise combined with cost, benefits and probability of success based on similar projects and life experience.
The recommendations, supported by facts (pictures and data), technical and financial analysis were dismissed by other perceived political priorities and interest which lead final decisions which didn't take into consideration the a.m. assessments.
My take from this experience which repeated in other instances is that technocrats and specialist assessments become irrelevant if the recommendations do not support and match the political interests.

This may sound simplistic, but based on more failures than successes, hire an experienced professional to create, promote and manage the online community, not just a part time grad student...

In Brazil, the Federal Government has been running a successful initiative called GNova (http://gnova.enap.gov.br/index.php), but it is not online. Last week, I had the opportunity to visit the UK Policy Lab (https://openpolicy.blog.gov.uk/about), with a greater online presence than its Brazilian counterpart.
I was interested in knowing how they work, to understand the relationship between stakeholders (for and against) and the success of the policy, but I could not come to a conclusion so far.