Not required ,In existing account only Tele-token solution can be integrated.

This integration follows One-One mapping, you’ll not be able to integrate 2 Exotel accounts with Zoho CRM/Bigin or Zoho Desk

Softphones are endpoints with a SIP client installed on them. This enables communication using SIP. This software can be installed on a mobile phone or a PC and you can use it to receive incoming calls as well as dial the outgoing SIP calls.

Yes

• Real Time Push: Using Events Callbacks, Exotel sends data to a webhook configured. You need to pass additional parameters in the Call/SMS API request with a callback URL. 
• Read more here: Calls | SMS
• Pull using GET API: If you have CallSID for a particular call, the details can be fetched using GET Call API
• Pull SMS details API:  If you have CallSID for a particular call, the details can be fetched using GET SMS API

If you already have a CRM to manage walk-ins, exotel’s experts team can help a way out to use Tele-Token solutions

• At the service level, the default maximum allocation duration is set as 170 days
• At the account level, this value can be configured from as low as five minutes until 170 days

The call connected via the virtual number to a cellular/landline number.

• Scenario 1 - Incoming call landing on a cellular/landline number.
• Scenario 2 - An outbound call made on a cellular/landline number via softphone