Hi Adrain welcome to the marine fish keeping
If you had a look in the marine section of this form you can see my posts, I had set up a 50L tank fir the first experiment.
As for equipment you will need:
Essential
Skimmer
Pump (to pump water from the sump/fuge)
Heater
Not Essentail (depends what you are stoking in the tank)
Chiller
Circulation pumps
PS. there are more things but then when you'll go more profesinal such as dose drimmper, wave maker etc can explain bettr on profeinal aquarium AM-
These are the basic, One usefull hint is to be patience, read and ask.
If you whant to come and see my aquarium you're welcome and you'll have a better idea of a basic marine and reef.
Goodluck
If you have messenger add me so we will try to meet.... camval88@hotmail.com