Ellison was due to return to Japan after the Mitre 10 Cup where he was an assistant coach with Wellington, but the Crusaders approached him to join them.
The chance took him by surprise but he felt it was a massive opportunity.
It had all happened quickly after Jones' decision, and Ellison said he was still getting across all the information but receiving support.
Crusaders head coach Scott Robertson said having a full coaching complement allowed him to step back and see the bigger picture in the role.
Ellison had been in several teams under many good coaches and would bring his flavour to the side, Robertson said.
Ellison said he knew from friends who had been through the Crusaders' set-up how good it was and in the short time he had been with the group he realised players were self-driven and open and willing to learn.
He said he had always been interested in coaching during his playing career and had learnt off some good coaches.
Jamie Joseph, for Wellington and the Highlanders, Wayne Smith, with the All Blacks and Tony McGahan with the Melbourne Rebels were coaches he mentioned who, while they all had different approaches, demonstrated different angles he found important.
Robertson said former Blues centre Rene Ranger had joined the side as injury cover.
"Firstly, Rene is playing some sensational footy. He knows his way around the paddock, has got his style, [he] brings a bit of uniqueness.
"We've had some great players from the far north come and [who have] left their mark on the team. Norm Berryman, Norm Maxwell, he's got that good laid-back nature about him, but he can turn it on when he needs to.
"He's a good inspiration for the young fellows, he will get around them, still does his work, he's good enough," he said.
Backfield utility Josh McKay had dreamt of playing for the Crusaders and would get his opportunity after moving from the Highlanders.
"When he had his opportunities for the Highlanders he was pretty sharp and was pretty incredible over the Mitre 10. That's why we've taken him in," he said.
Coaches had given him a programme to put on some more weight and things to work on, and he was already showing the benefits of that work, Robertson said.
He had a work ethic, and the timing was right with the injuries the side had suffered. Wing George Bridge would be available by the second round of Super Rugby Aotearoa while centre Braydon Ennor would be out for the New Zealand leg but expected back for the trans-Tasman competition.