I need to know 3 things about operating a retail party-supply store (brick-n-mortar, not online). If you would, please share your knowledge or experience.

The store will be located in a primarily commercial area, so a lot of lunch & after-work business is expected. The building is a standard 20x50 suite (1000 square feet) with a small admin area in the back, leaving about 800sf of retail space. The inventory will be basics (solid-color paper plates, napkins, plastic table clothes, flatware, cups, etc) plus some specialty & seasonal.

I have everything worked out & plugged into the business plan's financials EXCEPT for the following:
- Initial (start-up) inventory costs
- Monthly inventory replenishment costs
- Average mark-up

With these 3 pieces of information, I can calculate monthly revenue, and finish the busines plan.

Thank you in advance...

PS: if you would rather, you can PM me the info.