Alright, this is what I've been thinking of lately:
You start with 1000 Ore Storage (built into the system). (I might change it to 500 or something, because ore gathering isn't like OP2, it takes longer to get ore. But bear with the figure of 1000 for now).
This means you can have 1000 combined ore on hand and in the bank at any one time.
You can increase your storage by 1000 each time by buying a Storage Tank (like in OP2).
If the storage tank(s) get lost or sold your storage decreases 1000 for each lost tank.
If you hit your max limit you cannot gain more ore, or receive ore from others until you buy another tank.
When a storage tank is lost or sold, any ore that is in excess of the new limit is lost. (Like in OP2. For example, you had 3000 Ore, and a max limit of 3000 as well. Then you sold a tank so your max is now 2000. The extra 1000 ore gets lost because you cannot hold it anywhere).
Smelters: The idea of smelters seems good, that it increases your ore per post by 1 for each smelter you own. I don't think that it should have any built in storage like OP2 has however... because you already get one beneficial effect...
As for mines, I don't really know what the best way to implement those would be, because you get ore for posting in any forum that counts posts currently (which is every forum except the test forum, afaik)
As for rare ore, I don't think I'll get around to that initially. It might come someday but not any time soon. (It would be a lot of work to handle rare ore).
I want to get the ore stuff dealt with before I go on with weapons, etc.
So post your comments and suggestions.