With my experience with the MPB's and the few strains I have grown in them I feel it is best to clone your mother plant into 6" RW cubes in week 5-6 of the current bloom cycle, have them under a 1k watt MH within 10 days after you clone them. Start the 1k 24" or more away from the clones and drop the light as they can take it. Let the clone veg on the table in the 6" RW cube under the 1k MH all of week 7,8, and 9. Then harvest, bleach every plastic part of the system, flush the system with plain water until you can drink from it. Then the clones are ready to be put into the system, they should be roughly 12-15" Tall and 8-10" wide. You wont get the width on your unless you use the 6" RW cube, I have tried other methods and the 6" RW cube is the best choice to use for many reasons. Once the clones are in the buckets veg them for 10-15 days. This should allow the roots to make their way down into the bubbling waters of the bottom bucket, once you have about 15-20 separate shoots into the bubbling water and 1 or 2 have the roots branching off them then you know you can flip. The plant should be 24-28" Tall and 30-36" Wide at the time of the flip, the root zone is just as important to watch before the flip as the size of the plants are, they go hand in hand. They key factor to getting your plants to have a good stretch in the bloom cycle is to have the roots into the bubbling waters before the flip. I once tried to flip a set of plants before the roots entered the bubbling water and the stretch was no where near that of all the other times when I did things correctly. Following these steps my plants finish between 4' - 4'6" tall and 48"- 50" wide.
Hope this helps you further your growth into the MPB world
G