Major Ember upgrade - 1.12 to 3.5

In nearest future I will be doing a serious update of the application. I am not very familiar with ember.js & have no one who can help me with this material. The app is written in ember 1.12, and there are few dependencies. It has a web version and mobile (iOS+Android) written in cordova - all of them need an upgrade.

What kind of problems should I expect? How to prepare for them? How much time should I estimate? Any help will be very useful- it's first time when I will be doing app upgrade.

I have checked this links, but most of them are for above 2.0 versions.

https://www.emberscreencasts.com/meta_guide_to_upgrading_ember https://medium.com/ingenious/how-to-upgrade-ember-js-to-3-x-and-live-to-fight-another-day-cfc28c16b726 http://www.ember-cli-diff.org/ https://medium.com/front-end-hacking/everything-you-need-to-know-to-upgrade-your-ember-js-app-including-ember-3-9de5e808dde0 https://medium.com/ember-ish/upgrading-ember-from-1-13-to-2-8-0-f1dbcecc40ca https://medium.com/front-end-hacking/how-to-use-ember-2-code-in-your-ember-3-app-9ed15c28bad6