Well, first of all, keep it simple. It's weed!Yea I was also thinking about topping, but many people say it's absolutley not for beginners. Just one thing I'm curious about: Is it nessecery to top in a 45° angle? Or is that bro sience?
Imo no angle or anything special needed, not even a scissor. Clean fingernails are enough (for me).
If you want it sterile, just heat up a scissor with a lighter and do the cut.
Thats one thing I advise you...be a clean grower. Any type of organic matter that lays in a moist environment attracts mold - and we absolutely don't want mold. So keep your box clean.
You have to find your preferred way to grow and adapt the right nutes for that.
You can make mistakes with nearly any type of fertilizer, there's not that one magic thing.
Perhaps biotabs are easier (for next run), perhaps you switch to another vendor for another style of growing.
You came to one of the best places for advice, no "posers" here. Just ask, be a nice person and try to read through stuff here.
Cheers!