4-5 oz is about the minimum for stamping. I suggest buying the best tooling leather you can get your hands on. Wickett and Craig or Hermann Oak. The leather quality makes a big difference in the finished product.
But before you do this I have a suggestion. Pick a small item such as a key fob or bracelet. Make a batch of twenty at one time. You will get better time spent honing skills in batch work. You will get better hobby experience with a lot less leather. You could get an entire month of hobby time experience from a single shoulder or a belly.
If you botch a few, and you will, no great loss. Just save those as testers for the next steps in the process.
With one off projects you only get a small amount of time with each step. Something that takes two days to finish will only Grant you 20 minutes of cutting experience, 20 minutes of staining, 15 minutes of hardware, and so on and so on.
Doing batch work will convert each step into hours of experience. This will really help you get a feel for the whole process and really up your experience level fast.
Good luck and welcome aboard.