limitting the height of cannabis

I'm starting a grow soon and i need to know how to limit the height of cannabis. I'm growing in about a 2 1/2' tall space. I'm growing some seeds I got from a friend which are pure Indica, which is the shorter of the two genus's if I'm correct, but will still likely grow above 2 1/2'. I'm familiar with LST, but this is my first grow and don't want to try anything to complex and risk fucking it up. One option I'm considering is just skipping/shortening Vegetative growth and starting the seeds on 12/12 time, or starting them on 16/8 and switching them to 12/12 after a week or two. Would this work? I'm also wondering if topping them early/often would work, or if it would just result in less-then-desirable potency? If it would hurt the potency by how much would it hurt it?

Please, I'm new to this and open to anything. I'm willing to sacrifice the potency if it's necessary but obviously I'd rather not unless that's the only option.

Jah Bless, Gentleman