if you think of topping, what do you want to do with it after? how long do you plan on veging? how big do you want your plant? what shape you want your future bush?
General rule, leave the plant to grow for 5-6 nodes. Cut above the 4th and leave the 4th and the 3rd nodes to develop and LST them as they grow. The 1st and 2 nodes will be removed. Now you have 4 mains to work with.
Alternative, wait for plant to grow 4-5 nodes, cut above the 4th, clear 1st and 2nd and you will have 2 branches to start mainlining and manifolding.