There are a lot of options as far as headphones, monitors, and audio interfaces are concerned. Here are a few recommendations:
Reference Headphones:
Sennheiser HD 650 Open Back Reference Headphones:
B&H Amazon
Audio Technica ATH-R70x Open Back Reference Headphones:
B&H Amazon
Beyerdynamic DT880 Pro Semi Open Back Reference Headphones:
Amazon
Beyerdynamic DT900 Pro X Open Back Reference Headphones:
Amazon
Audio Interfaces:
Focusrite Scarlet 6i6 (2nd Generation, USB):
Amazon
Focusrite Saffire Pro 24 (Firewire/Thunderbolt):
Amazon
Monitors:
Focal Shape monitors (pricey, but excellent; sold individually so you need to buy 2): B&H, Sweetwater, Amazon