#1 - extensions are not authenticating directly to Vicidial, giving "forbidden"
#2 - failed to create the remote agents
#3 - Is not clear to me if we create the extensions in Asterisk and also with Vicidial ? Then DID's ? Is it ? need to rework ?
#4 - You have a "How-To" ?
It also does not involve "authenticating to vicidial". you create a "Phone" under "Admin->Phones" in vicidial which will dial to the extension in the asterisk box. this requires knowledge of "how to dial via SIP or IAX from one asterisk server into another".
The best method does not involve remote agents. but you can also create a remote agent. However, you will need to create the remote agent just as if you created the Phone in the above, the agent just doesn't need a computer to use the system, but the connecton to the phone is the same.
you may create a DID in your asterisk and call it with your vicidial server, there are several methods of dialing one machine from another. you CAN also dial directly to each agent (skipping the asterisk server entirely) if you understand asterisk. placing an SIP call does not require that you go through a server to get to a phone, only that you have the ability to transmit a packet on the appropriate port and have it arrive at the soft phone in question.
there are numerous methods and instruction sets for how to dial from one asterisk server to another and how to dial TO an SIP phone. google is your friend, i don't have a tutorial myself, but i've seen several discussions of the topic here and on most other asterisk based forums and wikis.
remember that the only real requirement is that vicidial be able to call the agent successfully, that's all you are trying to accomplish (when the agent Logs In). it does not need to go to a "provider" or through a "server", but if either of those helps you "get there", go for it.