Alright... just throwin' it out there.
From my view there definitely are not enough money sinks. Here are a few that would help regulate into later levels and not cause you tremendous grief at the beginning:
1) Equipment Durability - Have the ability to have heroes have smithing skill and repair your items to an extent. Have all equipment permanently decay with use so that eventually they are unusable. HOLD ON; now obviously to balance this you need to reduce the cost of items significantly and have higher quality items decay more slowly (that's part of their quality). Smiths in towns/villages have maximum/slightly reduced ability to repair equipment. Everyone hates this suggestion but it's realistic and it will work, I promise. Only foreseeable problem is having to micromanage all of your heroes' equipment.
2) Make Upgrading Troops Cost Denars - This just makes sense in my mind. Where the hell are they getting all their new equipment from? And why doesn't anyone seem to have to pay for it? You certainly don't provide them with enough in wages to afford their new gear. Make it reasonable; 30 D for T1->T2, 60 D for T2->T3, 100 D for T3->T4, and 150 D for T4->T5. Keep in mind that that's just an EXAMPLE. Adjust for balance.
3) Troop Upkeep Costs - Troops already need food, but currently that's all. Why not have their equipment degrade from battle as well? You don't have to micromanage all their equipment, just keep it simple: give an XX% DUR rating to each troop type, and just to keep it really simple, have it just average out for all troops of that type at the end of each battle. Return to town/castle/village to recoup the DUR rating, perhaps spending a bit of time as well as denars. Obviously higher tier troops will cost more to upkeep. This even adds the sense of logistics to the game!
Clearly, balancing it will be the main problem. Economies are always tough to manage, but if you want a good one you just have to bite the bullet and make it work.