C++ expert here, mostly made games for Windows. I still didn't make any for xbox, but I'm keen on doing so. Since I'm just one guy making 3d modeling, texturing, rigging, animating, programming, music composing, sfx, etc. 6 months is too little for such a huge project of yours. I'm currently working on my personal project Shmup God, a shoot em' up game with complex models and graphics, I programmed the pixel-based shader as well in CG, that's C for Graphics language, similar to C, but specialized in programming GPU, and after working on it for 5 months or so, not every day, but let's say there's about 2-3 weeks of effective work during that period, it's only roughly 2% of the game finished. Your game is of bigger complexity, so it would take much more. I'm also an AI developer, so artificial intelligence is my thing and I can tell you that only for AI development it would take more than 2 months for your type of game (unless it's a simple bot that doesn't provide any challenge), if you need bots that are controlled by server or locally.
Contact me with full details if you want to hire me.