Hey, cool idea in general. Though I would shift around the income structure a bit. Zerg unit from origin are fed to the meat grinder. So you need many to be effective. So basically a single zerg unit is useless. Those units should give income as it should be a trade off. income vs effectiveness. Protoss units are known for their rebustness / effectiveness, and terran units are something in between.
Its like with building mines to early with the desert strike game in the arcade. If you build one to early the enemies might have more units which will enable them to get the bunker faster = more income to further snowball their unit count, they will have the middle longer, etc etc. The trade in your game should be the same I feel like. And it would be cool if you could follow the lore of SC a bit on that. Protoss units = costly - Terran units = avarege - zerg units = cheap
Hope this helps :)