Hello, I'm a python expert with a background working for amazon and as a CTO for a large social media app.
I don't believe your project should take 6 months from a functionality standpoint, perhaps around a month at most.
I have no problem using flask with whatever js libraries you want to use, I'm assuming you will want to deploy using docker+nginx. Alternatively I could use twisted or tornado to make sysadmin easier with less moving parts and potentially better scaleability or even django to take advantage of it's inbuilt administration features. I would say django would be fastest to turn around a full product and tornado would take longer but be better suited for performance, of course the decision is yours.
As for project flow, a trello board is fine but for the greatest efficacy I would suggest also preparing a full specification to keep the project on track and reduce the need for micro management which I'm sure you would rather do without, of course feel free to review my code.
It sounds like an interesting project and I look forward to working with you.