I’d hold off nutrients of any kind until the plant is beginning to look hungry (lighter green leaves, sometimes in distinct patterns). As @Underthestairs and @Covertgrower mentioned, Miracle Gro is somewhat unfriendly to cannabis and FF Ocean Forest is pretty heavy on nutrients by itself. I wouldn’t be surprised at all if you could make it 6-8 weeks into the grow without needing much beyond some extra CalMag along the way.
Welcome to the community, by the way. I’m not an auto topper, but I do FIM them - it looks almost exactly like the photo @MeEasy shared, just move that yellow line up about 8mm and you’d have the difference between a fim and a top easy.
First time grower here too! Running a little experiment with white widow autos to see for myself how the yields differ, if at all. If you look at the middle row of four, the two ends have been left “untopped” and the middle two have been topped (one because of an accident and one just grew a bizarre multiheaded stem). I’ll try and remember to keep you posted! So cool how they look so different trained vs untrained.