How do people form big colas? If I LST the main to...

If you want to use the topping and LST'ing method then you don't really want to use auto's bro, as they don't spend long enough in veg to utilize this method. I would just LST auto's and let em grow, otherwise I would use seed's that you dictate when to flower by photo period. As for this plant I wouldn't do anything now just let her grow !!

There is a couple of ways one is outside under the sun with full sun and plenty of fresh air. Another is inside with plenty of light 1000w hids and co2. The last is by concentrating the plants energies into fewer branches. So instead of 15 tops you have 1,2or3 tops that are the plants only focus ie sea of green type methods.

big watt lights (more than 400W) sunlight (outdoor or behind glass) combined with artificial light

In very simple terms: Big lights equals big colas. That and getting the ambient variables right, that been keeping the grow space in the ideal temperature and humidity range. Overall temperatures; above 23°C (73F), including the night temperatures, and ideally below 29°C (84F). If you want to get those colas that are 30 cm (12 inches) long and thick as your arms, you would need something like true 600 watts, be it HID or LED.