I would definitely use the skimmer. It's the heart of the filtration.
Imagine if you have 400 gallons worth of macro algae die off because of a failure and you're left with no filtration at all. All it takes is for the light over the macro to malfunction while you're away or something like that to kill off the algae. At least with a skimmer you can have some sort of back up filtration. It will also aerate you're water like surface agitation could never do.
Freshwater is a completely different hobby to marine. You can be the best cichlid or discus breeder in the world and still not be able to keep a marine tank running. I'm sure you'll be a great reefer, but just letting you know only a small amount of experience is transferable to the marine hobby