I normally wait until the plant is 12" or so before my first topping. I also try to FIM instead of top but it often doesn’t work. (Topping creates two tops, FIM’ing does 4) When I install the plant in the screen I orient it so the four tops are on the diagonal and weave them out to the edges.
Doing a bunch of topping is at your discretion but isn’t really necessary beyond that first one IMO as the branches laid down will produce their own tops. What you do need to consider is too much canopy with respect to the root ball can unbalance the plant and it won’t thrive (too much canopy and too little roots)