Hello,
I can give you the consultant for what you need to ask. As the title of bid, I can give you some hint as below:
1. OS: you should go with centos if you plan using asterisk
2. You should install asterisk, freepbx seperately. Dont use some distro like freepbx, elastix, ....
3. Some techniques that you need to know before you start your project.
regards,
Vu Le