jhunter, I' ve never used an outfitter in CO but have taken one cow Elk there in three hunts. I learned a lot on those hunts and wished I would have used an outfitter first as a learning tool then returned on my own.
I preferred the last 10 days of the bow season. You have a better chance of cooler weather the bugling should be in full swing. Im not sure what the dates are this year but it always seemed to overlape the muzzleloader season.
You are smart to get into shape as early as possible. Do a lot of climbing the stiars and hills. If you can, do it with a pack on your back. The air is thin and the mountians can be steep.
There are a lot of good videos out there on Elk hunting but a good one to watch is Point Blank Elk. It' s all bowhunting and there are some good tips on what to do and not do.
Practice shooting from the kneeling position and learn what you can about metering. Meter in this case is... using trees, brush and such as cover by keeping it between you and the Elk, but not tight up agianst it.
If you have acess to a good laser range finder take it with you. The mix of the size of the Elk, unlevel terrain and clear air will make range determination difficult the first time or two out there.
And you' re paying a guide, listen to him and do what he suggest.