ecommerce Software for Amazon, ebay and Shop

Hello ladies & gentlemen,

I'm currently planning to start an ecommerce business in the U.S. and it is quite difficult to find a proper software to meet my requirements.
First of all, I'm from Germany and I'm working in ecommerce since 2010 so I've always used german software for my work.

Now I'm looking for a software which is capable of:

- synchronizing my eBay and Amazon orders with 1 click and synchronizing the tracking numbers after I've shipped the orders

- adding my new products to both platforms

- printing out my shipment labels easily

- send emails automatically to customers after I've shipped the orders

- handling returns with the software

- being able to be connected to a proper accounting software (needed aswell) so I can send the required information to my accountant without big trouble

- it must be able to provide me with sales statistics etc.

- preferably it is a software which is properly installed on my Computer, the database can be hosted online though so I can access it from every computer I have a software on

- preferably not a system which runs in a browser, I have made quite bad experience with that

- also important is a system which also offers a webshop which is connected to the database so I can also get the orders from the Shop quite easy

- the shop-software should have SEO tools and some marketing tools e.g. google Shopping, Adwords etc.

- it also needs to have a system for the Sales Tax issue, this is very important

I have worked with JTL here in Germany which is a great system but it won't work in the U.S. properly due to the distance between my computer and their servers.

Hopefully you guys are able to help.

Best regards