You got a pretty mix of different game kinds and genres, which makes it really difficult to imagine a game. It is like saying, that you want to design a car which can dive, drive and fly and which is cheap enough, so that the middle class can afford it. Yes, it might be possible in the future, but I can't really see a way to realize it now or in the near future.

Best to pick up one core feature, you really find the most important, define it, write it down (GDD=game design document) and then try to extend your idea by adding more features to the core feature. It is important to actually define game mechanism, to write down a vision, how does it look like, how does it play.

To make it more clear, take the army feature of your game. Here are two, of many possible options:

1. Your army is only represeted by a simple number, which represents the army power on all of your land. You can buy new soldiers and the army counter increases. Combat is an instant event, the winner is calculate by the formula winner(armyA,armyB) = ...magic formula..., the winner looses 25% of his army, the looser 75%.

2. Your army is represented by individual soldiers, all have their own live, family, home. You can walk through your town like in skyrim, you can talk with your people. Combat is a massive battle where you can join, watching and fighting in a 3rd person perspective. You are the king, the ruler. All fighters will react to you in a special way, trying to protect or to kill you. Combat is executed in an interactive way, wounds are realistically displayed and will hinder your action...

As you can see, these are really two different games, which have the same idea. The first one is more a RTS game (which seems realisable at the first glance). The second one is more of a simulation, which will be much harder to realize. As soon as you add more features to the game, it gets ugly really quickly. The complexity will increase, game features will battle each other (eg from a RTS game view, you would need a top-down view with lot of number, from a 3rd person game view, you would prefer a more immersive design etc.), the vision will blur etc.

Of the different genres you are touching, the one you seem most interested in is PvP raiding and war of attrition, on a very strategic level of detail. The concern with being online to defend cities is hard to understand: it's obvious that armies must fight in automation mode as well as when they are guided by the player to avoid the need for micromanagement. An online player whose city is under attack could make last minute adjustments or counterattack, with only a marginal advantage over AI-controlled defense. If there is a hero representing the player's character, he needs to fight under AI control too.

Sounds like a game that is vast in scope and i think to stand much chance of progress you might have to simplify a little.

If you can split it down into stages you might have a good chance of completion.

I do have some questions though, firstly what do you plan to contribute to the game except ideas? Can you program, produce art or music?

If so what is your experience? Have you created or helped with any other game in the past?

This would help me at least in knowing what you are looking for apart from design advice and what we can help you with going forward