Configure Grandstream phones for Asterisk Elastix PBX

Hello there! We're setting up an Asterisk PBX using the Elastix Asterisk distribution and Grandstream GXP2100 phones. I need help creating an optimal configuration for the Grandstream phones, which may involve changing settings on both the phones and on the Elastix server. We want pretty basic things: transfer, hold, conference, open voice mail, page someone (both at a single extension and globally). We also need advice on if we should be using shared line appearance, where each incoming phone line gets a lighted button on each phone (which is what my users want) or a shared line pool (which is what Asterisk seems to support best). We're also having some problems with echo on the Grandstream phones. We're using the OSLEC echo cancellation software but are still getting some echo. Finally, once we've got a good configuration for the phones, we'd like to create a configuration file that we can put on the server and have the phones download and (at least partly) autoconfigure. Current configuration: Elastix 2.2.0, Digium TDM400 PCI card with 4 FXO ports, 2 incoming POTS lines.