Are there any issue of incompatibility with other modules?

I have a customer with 3 sites, with same items (all the inventory is the same) and they will love to have this so they don't have the hassle each time they have to update the inventory, since they have to add it to the 3 sites manually. They have a dedicated server but 3 domains and 3 different templates. How can I install this, integrate all 3 databases without loosing orders, customers, etc?

Also I have another customer that wants 2 stores but they are going to be in same domain. Can I use this module with subdomains based stores?

Your support is appreciated.