Thanks for the in-depth review and for sticking with all the early-days experience!
For now, there is no automated tracking of quantities sold and how much you have in stock. There is just a way for you to manually mark your item as out of stock.
About the products being posts on your blog, you can choose how you want to do this. One way is to instead make them as comments under some post, and another way is to post them in some community (or even make your own community) without them being in your main blog. Do these options sound like they would work for someone who wants to post a lot of products?
RE: A Look at PeakD's New "Store" Feature — A User's Out-Of-Box Experience