I've read that the very lowest branches are more difficult to root. So take any branch above that.
1) height does not matter at all
2) Cut any branch that has at least 2 nodes, and is large enough to work with. I've read smaller clones root faster. larger clones have a lot of stored nutrients that they can use before they figure out that they need to grow roots.
3) the active ingredient in rooting hormone is butyric acid. Any rooting product containing it SHOULD help get roots faster.
4) No you do not. My 1st clone ever was just a 4 inch branch in a cup of water. No gel, no powder, no bubbles, no H202, nothing. Just water. It took almost 2 weeks to root and I put it in dirt about 5 days after roots 1st developed.
My mother was cloned from a very small branch segment that had only 1 leaf attached. Basically it was a stick with a leaf. That little thing survived for 3 weeks in a cup of water before I added a bubbler and it finally made roots.
I was trying the branch segment cloning instruction from the GrowFAQ. >
Introduction
Most folks (including me) take only main growing tips as cuttings, but occasions arise when you want to preserve the maximum number of growing tips on the mother plant. Sometimes it is better to remove only one complete branch and make it into multiple clones. Occasionally, while training a plant, you will break off a branch. Here's a way to turn that branch into multiple clones.
Just as an aside, I discovered this technique when my knife slipped, and I cut across a node instead of trimming off the leaf and secondary growing tip at that node. I was surprised when the bottom half rooted faster than the main growing tip.
According to several sources, cuttings taken from below the main growing tip will usually root faster (and in my observation better) due to lower nitrogen levels and higher carbohydrate levels. I also find the stiffer woody stems from lower on a branch easier to deal with than soft green ones near the tip.
The smaller secondary growing tips will take a bit longer to develop into full fledged plants, but they will have a great set of roots to do it with.
Technique
Cut off the main growing tip by making a 45 degree cut through the main stem just above a node and prepare it as you normally would.
Cut up the remainder of the branch by making a succession of cuts through the nodes at 45 degree angles. You will end up with a bunch of short stems with a 45 degree cut at the top and the bottom, and a leaf and growing tip near the upper edge of the top cut.
If the cutting is too long to fit entirely inside your cloning medium, trim the bottom end of the cutting.
Holding the cutting by the leaf stem (petiole), scrape away some of the outer layer of the stem tissue to expose some phloem (the white tissue underneath). Dip the whole stem into your cloning gel or rooting hormone, be sure to cover both the bottom and the top cuts. Avoid getting any on the growing tip.
Insert the stem into the cloning medium, you may need to open up the hole in the rockwool or latex plug a bit first.
Use a sterile tool (a chopstick, q-tip stem, etc) to push on the top of the stem to push it inside the cloning medium. The leaf may tilt up as the stem goes inside the medium.