Maybe this page will provide some pointers
From the documentation Support topics there are migration pages, for instance Migrate your data from Google Cloud to Murena cloud.
Use of a OTG USB Flash drive can be useful for transfer of items in your regular internal storage from one device to another.
Regarding your SIM card which you have been using in regular Android, there are some who would feel that this card and phone number will be already “known to Google” and so they would prefer a fresh start.