is it easy access to and from main airport and do you have a tour office on site or near by?
The access is easy, if it's your first time or to reduce the stress, pre-pay a private car service for the transfer. I used amigotours, they were very reliable, professional and friendly. The trip in was at 4pm and took about 40mins, the trip out was at 6am and took 15mins. For tour ideas, take a look at viator website for Mexico City.
Depending on traffic 30 minutes to 1 hour depending on the time of day you depart from the airport. Remember your pretty much downtown DF at the HI Express. There is a tour company right next door at Plaza 222, the mall (shops/restaurants). The tour company runs the double decker English buses for their tours.
Get an answer from Holiday Inn Express Mexico Reforma staff and past guests.