Has elemental established a basic economy model yet? I think the game won't really begin to take shape until they have settled down on the basic way that money and resources are going to exist in the game. Here are a few of my suggestions.

Firstly, in a 4x game, having a strong abstraction is important. A player has to feel like a leader, and make leader decisions, not micromanage the number of bricks and sheep they have. If a player in a 4x game ever has to look and see that they need 4 more units of wood and 2 more iron units to create a troop or building, there is a problem. But this must be balanced with the fact that complexity and options are a good thing, so managing many resources is desired as well.

Many 4x games model this by using a 'Production' abstraction. I think what seems to be in the dev's eyes is taking this "production" value and making it mean more, by having resources and items to go along. I think one way to do this, is to abstract out the 'production' into several values, yet equal one.

Creating a unit or building should cost two resources. Production and Gold. Gold is simple, gold is gold, done. Production is now slightly more complicated.

Each city should produce x amount of production per turn. The amount should be a total of (City Production + Empire Production).  City production is a sum of all the production generated from the local city in terms of the buildings and resources that it contains.

Empire production is a little more interesting. This is where controlling resources such as mines factor in. Before I explain further, lets take a look at how this ties into unit create.

Since a unit costs Gold and Production, each item you place on it will have a certain gold and production cost. Since production is too vague, lets break production into several categories.

Stone production and Iron Production. Now, if I put stone boots and an Iron jacket on a guy, it might cost 2 stone production units and 5 iron production units to make this troop.

So lets pull back out to empire production. I might control 5 stone mines and 1 iron mine. Each stone mine will yield 10 stone production points, each iron mine will yield 10 iron production points. So in my 'empire production' I have 50 stone and 10 iron production.

Now, each city should, based on things like road connectivity and building types (tradehouses etc), be able to tap into that empire production bonus. Now lets pretend I need to make a ton of this troop that needs 2 stone and 5 iron (based on the parts he is wearing). Each turn a certain amount of unit will be built based on the production.

First you use all the cities production into the unit. Then, you look at the empire production (ie the prevalence of certain resources in your empire) and start producing based on that. Now it will get slightly complicated. So, lets say it takes one turn and we have done 2/2 stone production, and then I used my empire bonus and 2 of 5 parts are done with the iron.

On the next turn, the unit should be finished, as even though due to empire resource production bonuses I can only make 2 parts of iron per turn... the city production should abstract, at a REDUCED level, into the iron production cost.

In this way, if I have an empire with iron armored troops, controlling iron mines makes me able to churn them out faster then someone who does not, but that person who does not have them, is not left in the dust, unable to even make iron units, he just gets no empire production bonus.

Going further with this now, is what happens to resources when they become outdated? Eventually nobody will be using stone, what about all my stone mines I fought hard over? There should be a series of sliders for each resource type to deal with this (or even automatically). Every excess production that is not used that turn, is converted to gold. So, if I had 100 units of stone production that turn, and there are no stone troops being made, stone will have a ratio of production to gold, and be converted. As soon as I start to make a giant castle wall, that the stone will all be moved into that project, giving the stone production bonus and not gold.

Finally, since this game has magic... I am not sure how it will fit into the economy since I am not sure what the devs have in mind for magic's management. But one way to deal with it is to have a similar model for for different magic types factor into your channeler's magic power. In that case, substitute production above for 'mana power', and I think that is a viable model for magic power.

I think creating it this way will give you a way to have many resource types, that have value, without being overly complex to manage.