1st Century Roman Leather Pouch Link

[Martin Moser]

Which brings me to the next question: what is the best kind of leather to get for this? I don't want anything too thin, and nothing too thick that it would be difficult to work with ...

Romans seem to have used a lot of goat for things like this (alum tanned leather is more resistant to tearing than the veg-tanned variety), so this should be first choice. Sheep is possible, too. If you want to carry a lot of weight in it, you should consider cow hide.