Very nice image, great effort and I'm sure it's much better than I could do as I have hardly worked with composites. I love the leading lines of the huge duct work and ceiling construction and their reflections in the pool. A few places to perfect:
1) If you're going to go for the "straight on" perspective, you better make it perfectly straight on. That is, place the subject exactly in the middle of the two starting blocks, level your horizon, and make sure that you yourself are exactly in the middle of the two starting blocks and that your lens is perfectly parallel to the edge of the pool. When you get it exactly right, you REALLY suck the viewer in with all of the perfect symmetry and leading lines.
2) There is a huge difference in contrast on the left side of the frame and the right side of the frame...I would even that out more. It almost looks washed out on the left from some sort of flare.
3) You're lacking light on the bottom half of the subject…this may not matter too much, but if you plan on capturing any more than what you’re showing with your sample here, it will only look much worse.
4) I would get rid of the numbers "5" and "6" on the starting blocks as they are irrelevant to the individual portraits. This may seem overly nit-picky, but if you're going to use 1 background for all of the individual portraits, you might as well make it as good as it can possibly be.
Good luck and have fun with it!