EBay/Zen-Cart/Drop Ship Solution

Hi

I was wondering if anyone had any ideas about how best to structure something. I intended to pull together the following:

1.) A business that drop-ships products for other retailers. I want an online store than handles each transaction, i.e. takes the details from the retailer and processes the order. I was intending to use a modified Zen-Cart system for this.

2.) I have an existing retail business (running Zen-Cart) and want this to go through the same basic process that any other drop-shipper would, i.e. all of my sales through this channel will be processed by my drop-ship business/process.

3.) I also want to pass sales through EBay and have them dispatched by my drop-ship business.

I therefore have two channels for retail sales and want both sets to be handled as if they were any other drop-shipper placing orders through my drop-ship business. The idea of having the single back-end dispatch business is to keep track of stock in one integrated place despite the multiple sales channels.

The question is how best do I structure this to make processing orders as straightforward as possible. I do not really want to be picking up orders from Zen-Cart (retail) and typing into my drop-ship Cart and similarly this seems a pain to do something similar with EBay. I see a number of tools trying to integrate EBay with Zen-Cart which might be useful.

Has anyone done anything similar and who could give me some advice please....

Gary