?#1:Should you top a indica plant at 2 ft for bigger yeild
If the question is, can you improve yield by topping indica plants, I believe the answer is "yes", though by how much (if at all) is going to be highly dependent on individual grow circumstances.
IE, are you growing indoors under lights, or outdoors? Do you have room to train your plants? What are the growth characteristics of this particular strain, etc?
Note that topping plants will, at least temporarily, stunt their growth, so consider this as part of your equation.
Its not just yield per plant, but also yield per plant per unit time that matters if you're growing indoors.
?#2:Is it better to let grow to maximum height for bigger yeild
In general, the bigger you let your plants get, the more they'll yield.
But there are practical limits here.
For example, if you're growing indoors under lights, you've probably only got so much vertical space to work with.
Outdoors, the limiting factors to size are going to be strain type, pot size, and length of season. The biggest plants are started indoors under light, so they're already well-established into rapid vegetative growth by the time they're put outside in the spring.
Also, in terms of yield, absolute height of a plant isn't as important as number of flowering tops and strain. A short fat 3 foot "bush" with 5 tops may yield more than a 5 foot "beanpole". You can bend/train plants to reduce their vertical height without any practical decrease in yield.
?#3:Is thier a way besides the two options above, to obtain greater yeilds
Yes.
The easiest is to use a higher-yielding strain.
Second easiest is to grow more plants in the same space.
If you're talking about indoor grows, "sea of green" is a way of growing large numbers of small plants to create a forest-like canopy to maximize light usage by flowering tops and therefore yield.
"Screen of Green" ("SCROG") is a way of accomplishing effectively the same thing by training the tops of smaller numbers of plants into an even canopy using a large mesh screen as a trellis.
Outdoors, I'd consider topping more than once.