Okay considering I spent a few years in the leather industry I should share a few secrets.
Cutting leather....
Whats this I hear about stanley knives.........Get yourself either an axe, ulu or saddlers cutter. At a primitive level.
If you want top notch and more modern get one of these.
The good ones aren't cheap but will last years of constant daily use, while I was working for over three years, we went through about 15-20 blades a year. And I wasn't the only one working there. The very best ones can be bought at john lewis or similar fabric supply shops. The blades are japanese and are very good, you won't even feel it cutting through 5mm leathers. The main reason ours didn't last long was a nick into something other than leather eg ruler on table. If cared for one blade should last you a year minimum.
DO NOT get the large spring version. get the 45 or 60mm version.
Glues
One of the best glues in the word is italian rubber glue. You spread it on with a spatula type edge, It dries in minutes to a sticky consistency, apply both sides and then join, once solid it is virtually impossible to seperate without getting a very good grip on it.
Leather cutting matt
Go to a kitchen/carpet shop and get a small bit of the toughest lino they have. 2mm is ideal. Glue it to a table top and work away. or use lino squares from a cheap shop.
Ruler for straight edges
Get a 2-3 inch wide aluminium or plastic one made for it about 1/8th inch thick, regular metal rulers work, but too thin might lead you to make mistakes.
Marking lines on leather
We used a marking crayon, it's not regular wax but I am not sure what it was.
We mainly used sewing machines, I would recommend it, but it's not an option for the hobby maker, so use the others suggestions.
What I use are nails, hammered through wet leather to avoid weakening, an awl is a decent working tool but very hard work by comparison. Using pliers for grip does help here though.
If you want to use thongs as I do, because it is more of a craft than simple stitching then you will need a hold punch. I have one multi sized screw on set which was cheap and I also have a japanese 2mm hole punch which has been going for over ten years, and will last another hundred for the hobbist.
Thong cutter, these can be bought quite cheap, the blades can be sharpened fairly easily with pliers and a stone. the material used is weak so wax the leather first to remove friction which will cut into the plastic other wise.
hope these few tips helps you out.