What are the common footprint naming conventions

Every EDA package will handle its library differently and also, within the tool, it's likely the libraries are not consistent. In the CPOL library in Eagle, you can see in the 'Description' column things like 'E5-8.5' - this corresponds to a radial capacitor, 5(.08) mm pin spacing, and 8.5 mm outer diameter. So, in this particular library it is: E[pin spacing]-[diameter]', with dimensions in mm. You've searched as far as you can, so you just need to select manually now.

This is just the way things are with tools as there's not really any one obvious good way of doing things - there are a lot of components out there. You just have to accept it or get annoyed (and only one of those gets things done..).

IPC has some footprint naming convention in place. Have a look at Mentor Graphics LP Viewer, The supplied libraries implement the IPC schema. Footprint naming convention is a prime example for XKCD 927.