SQL or NoSQL? It's probably not really as important as it used to be but it does drive how things will be structured. It'll be something to figure out early. I've always worked with SQL Database Engines in enterprise environments. Large monolithic solutions tinkered with over years to adapt or integrate to the changes in the ways of working. Usually dependent on obscure workarounds ticking along unnoticed, long forgotten and whose authors have moved on long ago. All whilst being clearly and concisely documented in that print out that was lost in the last office move... Being able to fill in the gaps based on the rules implemented at the database level brings forward stories rediscovered and forgotten with every project. When it's your own work and a single application creating data, I think we'll manage either way.
We've had the idea, we've spent countless hours discussing the potential of this endeavour, the excellence of Guinness, and what we'll do when we are gloriously rich. Next steps coming soon, watch this space :)