Henry, I figured if it was just you, and you wanted to test the game idea quickly. You could do it on paper to see if it was fun. Of course, I don't believe that would work well to simulate everything needed for an actual video game (esp. something as compelx as an RTS), and yeah, if you can find an engineer, then you could built a prototype.
My worry is that an RTS is a complex thing. I don't know other mobile RTSes, but if you are talking C&C or Starcraft, then there's level building, unit AI, pathfinding, a whole host of UI related gameplay stuff (tech trees, maps, waypoints, etc.), other UX and then of course, doing all of this on a mobile device where my attention span is that of a goldfish. If you can do it digitally, and want to build it fast, prototype the core gameplay mechanic you are going for and learn whether or not that is fun as a first milestone. Check out Unity 5 since it does a lot of heavy lifting tech-wise and it's cross platform -- you can get your app on Droid or iPhone (you don't need the $99 sub to test on a local device, so I've heard from Apple's press conference last year). Make some simple 3D assets in Blender for testing purposes, script up the core game loop and iterate over it until you get something you like. Do all of that before you invest your money and someone else's time and energy in making intricate art assets and whatever. Uniqueness counts, but also craftsmanship too. Build a game that feels fun and runs decently, or why would I come back to play?
You may also want to get your hands into Unity, if you're running with 1 or 2 other people -- so that's something to learn (via Youtube). There's other things to do rather than code. While your engineering guy is doing that heavy lifting you could be figuring out tuning, or making temp assets, world building, etc. Don't just rely on the design doc; it's not the ten commandants. Nobody reads that doc anyway and it'll probably be obsolete a week into the project. If there's an idea worth it's salt it's in the game prototype.
I don't want to say, "don't do this," not because RTSes are niche, but because this is the first time you're going to try and make a game at all. Every guy who has an idea for a game always wants to do an RTS, or RPG, or open-world MMO Minecraft blah-blah thing. Yeah, Notch built Minecraft himself up until alpha, but there are plenty of cases where folks are over-ambitious and have no idea what they're getting themselves into and lose all their money (look up the Kotaku article on the Yogscast guys and their "minecraft" clone, it's worth a read on a failed Kickstarter project). If you're going to do this, spend some time prototyping with a small team till you get something that works, scope to have a minimal feature set, and don't feature-creep/add shit to it unless you absolutely have too. Get time estimates in days on features when you're ready for production and multiple them by 2 or 3 because everything will go sideways, and that's how much time you'll probably need to finish the game. Don't forget to add time for beta testing and bug fixes.
Good luck, man. Game dev is hard and time consuming, but it can be fun to create something from nothing.
