How many times to top depends upon your space and time constraints.
When I am not pumping out breeding plants, I veg a plant to fill a 4x4 trellis, so I can pull over a pound.
How long that takes depends upon the plant I am vegging.
One of my favorites is a Kosher Tangie that has medium internodal length, but is so flexible that I can weave it through a trellis to use every inch of space.
I will sometimes veg for 10-12 weeks, and pull enough to leave that clone alone for months.
But I have indica's that will just sit and waste time rather than getting bigger. If I top them once I lose half my weight.
Usually you just get used to what you have, and make personal choices due to grow size and time to grow.