Android based Order Management system

We are a company that sells automobile parts. We need a order management system whose front end is a tab, and back end is a linux server. The android app needs to run on tabs and will do the following. 1) Sales representative will choose a sales port and give it to a user. User cannot exit the app or go to sales port selection screen. If someone needs to goto home screen/Sales port screen, user must enter a password. 2) After selecting the sales port user will see a carousal of categories (4-7 categories in one screen) with images at bottom. 3) After clicking a category, a grid of sub categories with images will load in upper section. (Assuming the category carousal will take 20% of total height). 4) After choosing the sub category, a pop-up/modal will open, with carousal of products(4-7) with images at bottom(similar to categories), and above section will display image and description, price of product. User shall be able to navigate to next product like we navigate images in gallery. The product page will have a text box, allowing user to enter the quantity and a button to add to cart. Also there should be a button to close the popup; Once popup is close, user shall be able to see carousal of categories, and grid of sub category. Other important information. 1) Admin can add delete any number of sales ports. Sale port will have a name and id. 2) Admin can change the categories, sub categories, product images, description, price etc. And on request from tab, the catalog should get updated with new information and images. 3) User may submit order multiple times, without requesting for invoice. Every time the user submits the order, the ordered items cannot be changed, only new order is appended. 4) Once payment is requested, then invoice will be printed at the server printer. 5) User should have a button to request assistance always visible on all screens in the app. The functionality of this button is not in scope for now. But please create this button. Please refer to network diagram and flow chart for more details.