I'm glad that helps!
R500 APs will potentially give you better performance but it depends on what type and how many clients you have and the environment they are operating in (interference, multipath, etc,). Also if you have all R500's then you can move APs around or have a single spare in case of an unlikely failure.
However the list you mentioned will work fine. I've changed the description to reflect our terminology - (apologies for not doing so properly in my original message):
1x R500 Root AP (wired ethernet)
1x R500 Mesh AP (wireless mesh)
3x R310 AP (wired ethernet)
The Mesh AP has to be within range of the Root AP, which in the mixed-model scenario above must be an R500.
Yes these APs will not only work as one network from a client point of view but will also be a single network in terms of management. The point of Unleashed is that you configure a 'Controller' AP and this will push configuration and provide management and monitoring for all the APs on the LAN. You can deploy multiple SSIDs and any client connected to an SSID you've configured will roam seamlessly between the APs, providing you have sufficient signal overlap.