Hi there!
Topping is a great way to begin any training routine. Topping with no subsequent training doesnt really achieve much, in my opinion. When to top also depends on a few factors, such as;
how long you plan to veg, your maximum grow height, and the strain.
Topping followed by training can result in a more even, lower profile plant, which is usually a good thing. If you plan to train and want to flower asap, I would top the next node, and begin to train the two branches out horizontally. You could also wait another node or two, doesnt really matter much. All in all, thourough research on the topic is worth its weight, I've just scratched the surface here. Hope this helps, cheers😀