all great questions. I've ran a lot of communities like that. I use spreadsheets or Asana to manage. I'd advise you to use whatever system is embedded best within your team, to make collaboration easier.
2. sourcing ideas: survey customers, listen go Gong calls / summarize them with AI to understand key trends, ask CSMs / whoever you work with on account teams. I like to also get embedded with CS so I can learn better from them (I go to their all hands meeting and team lead meetings).
3. prioritization is always an art and science and is in the eyes of the beholder / whoever funds your programs. Researching ideas and pain points in (2) can help you nail down what's urgent and what can wait. Have a clear content calendar where people can see what's coming when, and if something needs to be lifted forward, have a negotiation.
4. ideally SMEs.