FFOF just has more nutes in it so you can get away with straight water feeds a lot longer. Like 3 wks to a month I think. Promix has a starter fert charge and is good for a week or two tops before you need to feed it, Its much more soiless hydroponics than FF is.
Promix would be my preference, but I'm a control freak lol. But by the sounds of it you are looking to do basically what MiMed does, and by all accounts it's an excellent way to go.
The problem with potting soil that is ammended like ocean forest is knowing when and how to ease into fertilizing when the nutrients run out. And with the nutrients activating in the soil overwatering becomes more of a problem as well.
As a new grower I found pro mix hp easier to manage. And it taught me how to watch the plants and better know when to water and how to fertilize. Mistakes are easier to fix in pro mix than ocean forest.
But to water only you can keep transplanting up to larger pots with new ocean forest and have a few weeks of nutes available each time.