email him the file and he can transfer to his device,you should be able to share with bluetooth between the 2 devices but i have never managed that tbh.
pretty sure bluetooth transfer will not work on the 660. to transfer a route using your pc to his nav 5 would be the same as you do with the 660, if you mean how do you get it to him if you do not have his device, that would be as above and e mail it to him, he can then copy and paste it into his gpx folder on the nav 5 if he does not have basecamp or mapsource.
Yes. the only problem you may encounter is if the settings and preferences are different on the nav 5 compared to what they are in basecamp, your route may alter when it is displayed on the nav 5, so just check the preferences and then the route after transfer.