If Unity3D isn't suitable, you could use XNA. With your time budget, I think you could reach your goal without too much pain. Though, you'd have to recreate engine features, like particle engines, which come out of the box with Unity and is quite powerful.
Thanks, mate. I'd consider XNA, but I'm already off to a good start with Panda3D, which features a built-in particle system.
Unity3D is my first recommendation. You can get something up and running pretty fast. Admitedly though, I'm not very experienced with Unity at the moment. I've spent about a week on it. I like that it supports C#, but the built in IDE just doesn't compare to Visual Studio.
I agree, Unity is a great tool. You can actually develop for it using Visual Studio if you buy the pro version, and I recall there being a klunky work-around for non-pro users if you're determined. The one downside, is to go beyond a prototype, I'd have to plop down $1,500. That would be acceptable if I had a committed project or someone was funding my development as in the past. That's less than ideal for a personal experimental project which may or may not turn into more.
I also have some Python code I'd like to use, and it's fun to see how another tool tackles the same challenges!
Edited by CuriosityKills, 17 November 2012 - 12:44 PM.