I've posted on the importance of knowing how to cut caramels, because recipes are really bad about explaining the way to go about it.
You need to do a quick non-stop sawing motion, basically. Put the block on the cutting board, butter or oil a serrated knife, and then saw strips away. If you stop before you've sawed all the way through, the knife will stick. Re-oil the knife as necessary and once you have all the strips, cut your caramels into squares or rectangles.
As for a thermometer, unless you're going to be making a lot of candy and jam, you can just get this. It works just fine and is commonly available.
The only thermometer that gets great reviews across the board is a thermapen, which is expensive.
As with any thermometer, you should test it to make sure it's properly calibrated, even when it's brand new.
Candy-making takes a certain amount of experience working with sugar, skill, and at least a moderate amount of luck, so don't get too discouraged if you don't succeed the first time.
But you know, don't test your luck and do try to make it on a nice dry day, not a humid one. Unless you're a masochist.