Check out Barry King for stamps. They are a relatively economical, yet good quality. I don't have any experience with his other tools, but I would be very surprised if they were at all lacking. I do use some Watt edgers, a creaser, cantle pliers, and a tack hammer. I'm happy with all of them, but they are not cheap. I have some Weaver "Master Tools" end-punches and hole-punches, as well as their round knife. They all work pretty well, but the shape of the round knife is not my favorite.
You can never have too many knives, but buy only those that work. If you know the size and shape of blade that you want, then buy the best (so, probably most expensive) that you can. Otherwise, try out a few different styles until you can distinguish what features are important to you. I have a Don Carlos large head knife also from Weaver that I use exclusively for skiving. However, I am not too impressed with it, and I wouldn't recommend it if you don't want to give it a fair amount of modification. I recently bought the new small Al Stohlman round knife from Tandy. Though I haven't used it much, it seems to hold a pretty good edge. The handle is poorly designed though, and needs to be reshaped. The round knife I use most is one that I made from A2 tool steel, so I would probably suggest going with a custom grade knife if you can. For straight knives, I primarily use the right hand bevel "marking knife" from Lee Valley Tools. It took some work at first to get the back flat and the shape right, but now it can slice 13/15 oz. skirting leather like nobody's business. I have the Al Stohlman trim knife, but I find the hawk-bill blade shape inconvenient to sharpen, so it mostly stays in a drawer.
With most tools, the best is simply that which allows you to do the job most effectively. So, I would suggest trying as many of different types and styles as you can before committing.
Regards,
Spencer