I live in Stortford. There's lots of two bed flats near the station, mostly very new, and more being built. Google should turn something up very quickly. Be warned, some do not have parking spaces allocated and parking can be pricey.
The Stansted Express goes to/from airport and Stortford - one every 30 minutes normally. I'm not sure what time they start/finish but it will be on the website
www.stanstedexpress.com .
Buses run 24 hours - 510 from Harlow via Stortford to Airport is operated by Arriva - every 20 mins during the day but falls to hourly late and early. There's a few others but they tend not to operate late night or early morning.
If you look at the transport sections of the BAA website you will get most of the links.