Here is a reasonably well written description of someone attempting this trek.
My apologies if you have experience at altitude, but just in case:
For altitude concerns, drink lots of water and talk to your doctor about a prescription for Diamox prior to the ascent (need a few days lead time to have medication to be effective).
The rule on water is "copious and clear" for urine flow the entire day.
For clothing, the old adage of "cotton kills" is a good thing to remember. You will burn a lot of calories (and heat) as you go, but will get cold very fast when you stop to rest.
Some rules of thumb: altitude sickness can appear as low as 8,000'; for a walking trip, you can ascend about 1000' per hour at lower altitudes; about 500' feet per hour higher up; the temperature will drop 3 degrees Fahrenheit for every thousand feet of elevation increase.
I would consider looking around for fellow travelers who are similar in age/conditioning/level of interest with whom to do the climb rather than using guides, but that's just a personal preference.
If you do use guides, set your parameters with them before you pay or sign any contracts.
Some guides are very good and have the goal of getting clients to the summit. There are some guides who will take your money and try to run you into the ground so that you abandon the climb/hike and turn around (they get paid; you don't get any summit photos).