Hi UR,
There are certainly many unanswered questions about human evolution. As you study the subject in detail, you'll find that a number of your questions will be answered. The first thing to understand is that you need to discard many of your present notions since they were formed largely by misinformation from the Watchtower Society. Until I studied the subject in some detail, I had no idea how badly the Society has misrepresented evolution generally. The Society has borrowed bad criticisms from many sources, including young-earth creationists who have time and again shown themselves grossly dishonest in their efforts to knock down evolution.
A fundamental concept is to separate the fact of evolution from various ideas about the mechanisms of evolution. The fossil record is extremely clear: life has evolved over time, in the sense that life forms that once existed no longer do, and new life forms have arisen. That is the basic definition of evolution. It has nothing to do with whether the evolution happened entirely due to natural causes, or was guided by some supreme being. Similarly, the question of the origin of life has nothing to do with the fact of evolution as observed in the fossil record. One of the fundamental mistakes that the WTS has made is to fail to understand these points, and so it has caused a great deal of unnecessary misunderstanding in the JW community.
The fossil record of human evolution shows a change over time of the kinds of apes, apelike creatures, and humanlike creatures that exist at any given time. The earliest creatures that combine a few humanlike features with ape features were the Australopithecines. Their brains were a little larger than those of chimpanzees, but their hip and leg structure was a combination of human and ape. Later forms had very humanlike hips and legs, and were clearly capable of upright walking. Over time many of these died out, and new humanoids appeared.
By about two million years ago a species called Homo erectus had appeared. This creature had a body very close to that of a modern human, but the head was quite different. The brain was about 2/3 the size of a modern human's, and the shape of the head was so different from anyone living today that it would be considered grossly deformed. You can find pictures of one skeleton of a related creature, including the head, of the "Turkana boy" here:
http://www.talkorigins.org/faqs/homs/15000.html
http://www.inhandmuseum.com/LA/erectus/ergaster.html
This kind of creature is unexplainable in strict creationist terms. Down through the ages other types of humanlike creatures arose and then disappeared, and this is again unexplainable by strict creationists. You can find tons of information on various websites by typing "Turkana boy" at a search engine.
What is fairly clear is that the older the fossil, the farther it tends to be from the modern human form. Neanderthals seem to have first appeared around 250,000 years ago, and coexisted with creatures that seem to be the direct ancestors of modern man. They seem to have died out around 30,000 years ago. Cro-Magnons were identical to modern humans and so they have certainly not died out.
The problem of "where is everything in between" is not really a problem once you realize that more than 99% of all species that have ever lived are gone.
You have plenty to study, UR, if you want to really understand this stuff. It's very rewarding, though, and I highly recommend it.
AlanF