Your project looks interesting, I would like to help. I've implemented inventories management systems for a textile/garment industry and for construction business in my home country.
I think it would be advisable to put in a document all your requirements, as well as the assumptions and constrains, so that development can proceed smoothly. A system as described in your project has several concerns that need to be properly addressed - products catalog, POS system functionality, purchasing procedures, demand forecast, central warehouse system, to name a few.
I've written that type of analysis documents for several systems, and they can be a big help to establish the goals, deliverables, calendar and budget. Let me hear if you're interested in this approach by dropping me a line thru Chat. Thank you.