Please allow me my contributions.
I am particularly interested in point 4 though,
in the context of a local project I am participating.
No need to say, but I do: just my personal opinions :)
1.) A commons is a commons - a shared entity - air, water, an "allmend" (shared grazing), biodiversity, etc.
It's in the interactions of its users and their needs and accesses that its components arise...
(in other words I mean it's probably hard to generalize)
2.) Whatever organization its users decide to adopt could work...
Local cultural issues are very important in this context
3.) The "market" is like saying "God" - it's an intangible entity really...
It depends what you mean by it. A healthy community oriented market may be fine,
a heavily manipulated and controlled market maybe less so...
4.) I am thinking along these same lines lately. Local institutions (like NGOs, social help groups,
alternative educational orgs, art collectives etc.) with community projects should get free credit
to be able to spend in circulation on local service providers, and with sufficient diversity of participants
in the system, many needs could be served by members, making the units circulate.
But why would outside speculators want to buy stock from these groups?
If you specifically mention speculators, they are interested in returns only,
not in the community interest. Stocks often also imply voting power in the community,
so this to me doesn't seem very appealing. Also, where would these people
get their returns from? It would only work if they would be interested in returns
generated inside the community, which may be non-monetary...so there could be little incentive for them.
Things could look differently though if there would be a purposely sustainability/equitable stock market,
where investors wouldn't be interested in monetary returns foremost, but in supporting great communities,
and would be open on the nature of the returns. Still this could be done in bitcoins though (or something similar).
A very ad-hoc response admittedly so bear with me :)