I want to try and stay away from having another server if possible. AWS do have another option;
All my current instances are on the small 3.50 server - none of the sites generate an awful lot of traffic - these are small business that just want an internet presence. I could choose the $5 one to have both wordpress and magento running but I dont know much about the specs, would that be powerful enough?
When managing, how could I benefit from them being of a separate server? What type of management would be awkward if they were both on the same server?
A final alternative could be if it was possible to install two themes on one Wordpress site but maybe thats for the wordpress support team. One theme for my main site and then another just for the shop.