Not really much to teach in text form here. The Forestry wiki has in-depth information on how to assemble the multifarms, and there's probably video guides on youtube (Direwolf's Forestry 2.0 spotlight, if nothing else). I recommend burying the multiblock itself mostly in the the ground, so the trees above can grow unhindered while you can service it through a tunnel below. Just give it regular old oak saplings, the same ones you used for Steve's Carts. The moment the farm uses them, they get auto-converted to Forestry's genetic tree system. No tree breeding or manual intervention necessary.
If you're short on apatite, drop a quarry on top of an Extreme Hills biome. A good rule of the thumb is that one stack of apatite will get you roughly in the neighbourhood of 500 stacks of wood, or twice that if you have ash available for doubling the fertilizer recipe yield. Depending on the size you choose, a quad arboretum multifarm will consume somewhere between 2.5 and 6 MJ/t, ideally bufferd by a redstone energy cell (it draws energy in quick bursts followed by pauses).
The multifarm will probably generate slightly less (10% at most) wood and saplings per planted sapling than the SC farm, because apple oaks do not have the small chance to grow a huge variant that regular oaks have. Still, the output in apples is close to five times higher, for an equal amount of trees planted. How large a multifarm equals how large a SC farm in output, I cannot tell you. The 5x3x4 multiblock will give you the most bang for your buck in terms of upfront costs.
