water pump and timing belt are generally done together, due to the need to pull so much related stuff to get to either one, the cheapness of the parts and how catastrophic a failure of either one is.
You can find pretty detailed DIY's out there (check miata.net too), but its a big job and requires some precision to get it just right. You might consider contacting Steven AKA Rouge at Miata Solutions. Also, don't cheap-out on the parts or you'll be doing it again in the next few years.
As for "supervising" a job like this in 100 degree weather; good luck!