Fix a Woocommerce custom plugin and add custom plugin

Please, this is non easy work, so ONLY for Woocommerce, PHP and Wordpress EXPERIENCED programmer and with deep knowledge of PHP, CSS, Javascript too. We have developed a custom woocommerce Rental website, and we need to fix some issues in product page and checkout and add some custom functions. In product page we need to add the option to add more than 1 piece of the product (only if we have in stock more), so: 1.- We need to check the total availability and how many pieces available in the date range selected, then show the total number of products (in stock available in these range of dates) and an option to select the number of pieces (only available in the date range). 2.- Multiply the number of products selected X price of the product. Example: If the price of 1 product for the date range selected is $100 then for 2 pieces will be $200 and so on. 3.- When the user adds to cart, add the number of selected products to cart as well total for them, in the checkout the same, and after order, they will be unavailable for rental until the end of rental period is over, then they will be available again. 4.- Add the ability to change the number of products in cart, so the user before payment can adjust the quantity of products will be rented, based on the availability of the products in the rental range dates. 5.- Update plugin (the commercial one) to latest update as well woocommerce and wordpress and fix any problem that this makes. 6.- Fix the custom plugins/code to work with new (no major) updates of woocommerce, wordpress and used plugins. 7.- Add the option from the catalog page, search page, or any display of products page to click to add to cart (and make all the necessary calculations for total). 8.- Add the option to the Admin users to create in behalf any customer (existing or new one) an order of rental products, no matter the start date (actually the system blocks any rental before 48 hours of start), so we need to bypass this block for admin user. 9.- Display a Field of the DB value in the Pick Ticket of woocoommerce 10.- Auto-delete Start Date and End Date of users cookie every 24 hours Notes: The original commercial plugin we used for customization had the option to select quantity, but we deleted in our customization work, so you surely can use a lot of the "original" plugin to add this feature. We can setup milestones per task, these paid until full work is done, and we require at least a 3 months warranty.