It might be easier if you contact me directly at email@example.com, but to answer these final questions;
4. without looking at your config and troubleshooting further, I cannot tell you what the problem is.
2. As I fully explained in my previous answer, the model type will tell you how many T1/E1 ports you have and how many VoIP ports you have. You state that you have a DX2024, so this means you have 2 T1/E1 ports, and 24 VoIP ports, so the maximum number of simultaneous calls over IP will be only 24.