I'm a first time grower. I hardly have any height in my box about only 20inches. So i want to keep it short, but yield as much as possible. I read of topping the plant to keep it short. I was also wondering how to form more nodes, if topping does this? and if more nodes will make more bud to grow?

more nodes doesn't really mean higher yield, also, the only thing you can do is shorten the space between nodes (by having good light), you can't add nodes and make more by topping. topping make 2 colas come from where one was, but that's only because of the way the plant grows, not from the actual topping.

and I'll tell you again..... 20 inches is NOT enough room for what you want to do.

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my eyes always look like so if you dont like it! NOT GREED PEOPLE!

What i want to do is get as much as possible with the space and time i got. I read of plants being short and bushy so i was thinking thats the way i have to do it. If i turn the box on its side ill have room for about 2plants and itll be about 3.5ft high but my concern is with 12-14 weeks is this the best way and will they have enough time to grow. Or keep the box upright with 20inches high, can then plant more plants but they won't grow as good.

No contest, grow them tall.
With 20", you'll have to start flowering by the time they're about 8-9" tall in order to have any hope of constraining them to that size. And that's assuming you're talking 20" plus the height of the plants. Anything less would nothing beyond comical.

well i belive i u use a technik thet is saw in a nuter post(do not know witch one will post win i find it ) he planted his clon on the eage of his pot and during veg traind in tho lay down over the dirt it cud give you like 6" overall it culd work

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OF THE MANY or even
the one

train it horizontal when it's 16" tall(see my pics &blog).