The Very FIRST thing I suggest is you get a copy of this Book,
The Art of Hand Sewing Leather, by Al Stohlman.
http://www.amazon.com/The-Art-Hand-Sewing-Leather/dp/1892214911
This book came out a few years after I blundered my way through my first set of skins, knife scabbard and shooting pouch. I STILL refer back to my well worn copy that is now over 35 years old. Oh, I have never carved leather as it was not usually done in the geographical locations and time periods I am interested in, but this book is still almost worth its weight in gold for everything else.
May I suggest you not be tempted to use Artificial Sinew? The reason for this was it was first harvested from the laboratory experiments of the Bio Engineered Nauga from the 1950's, from which they also harvested Naugahyde? There was/were no natural wild Nauga (singular) or Naugaeen (Plural) running around in nature in the 17th through 19th centuries.
Oh, the above paragraph is a parody on using modern materials to make period items.
Basic Tools and Materials
1. Good Linen thread. Preferably Barbour's Thread. Also a small piece of Bee's Wax to lubricate it.
2. Good sewing needles matched to the size (number of cords) of your thread.
3. A GOOD Awl. The really good ones do not cost much more than cheap crappy ones and will last you for many years. Try the following link for ones made by Joseph Dixon. You will also need a good Medium or Fine India sharpening stone for them.
http://www.boothandco.com/handtools.html
4. A SHARP knife. Unless you plan to really get into a lot of leather work, I don't suggest you buy a traditional Round Leather Knife at first. I got along just fine for years with one of the Utility Knives that use the interchangeable "razor blade" type blades.
5. A good straight edge. I got along nice for years with a hardware store bought aluminum 4 foot ruler and a nice 6" machinist's steel rule.
6. If you are going to cut fringe, then you really need a good set of shears. On the first set of skins I made, I used a straight knife and it took HOURS to cut the fringe. A good set of shears takes a lot less time to cut the fringe.
7. Pattern paper. I used old newspapers for the first few years and then switched to plain brown wrapping/shipping paper. Oh, Graph paper comes in real handy for making knife sheath's.
Gus