Yes so basically it will work like this.
We will my oscommerce backend and ebay integrated.
You will create an ebay store with all my products and have inventory taken from my site and have them integrated in the sense where when something is changed on the site, it will change on ebay (i.e. price, picture, description or anything else)
After that all the orders placed on ebay itself will be transferred to my backend and I will be able to mark orders shipped, add tracking and everything else from my backend. I should also have an option to leave feedback on my backend as well.
Please let me know if you need any more clarification.
Shipping options, if possible you can put the same like on the website. Offer priority mail, UPS 3 day, UPS 2 Day, UPS Next Day. Do it based on weight and location if possible...
or the shipping you should also add USPS Priority Mail as a shipping option.
You need to transfer all the products and the categories and make the template all nice and neat. Make the template look much more professional.
With the products that Have size options you may add the product once and give the customer the option to choose which size he would like.
The prices will change as the sizes change as well. The ebay store should be exactly like my website with each product.