One of the most complicated parts of rts is the pathfinding. Take a look at intense-x zinc for this.

Are you really sure you want to go through with this though? RTS is one of the hardest genres to make a game on. You should really start small and gain experience before taking on a huge project like this. Do you have any teammates? you'll probably need at least 3 people to do this...

Sorry if i discouraged you, but that's how it is. I once attempted an RTS on my own.. did a couple of tech demos and that was it...too hard.