First How to Backup and Restore an /e/OS phone
then a forum search 
of Backup finds many results.
This (closed) post contains many useful links [HOWTO] back up your data and settings - draft.
Regarding Seedvault, go to
Settings > System > Backup > Seedvault Backup > Backup status
this gives a good overview of what is backed up. Bottom of the page includes Apps that do not allow data backup.
A backup of Contacts from
Contacts app > top left 3 bar menu > Settings > Export > Export contacts
A backup of SMS (recent versions) [1]
Message app > top left 3 bar menu > Backup and restore.
Make sure backups, including Seedvault, go to external media which will be readable by the new device.
Photos can be backed up to a PC by file transfer is probably the simplest.
[1] if the option is not available, perhaps try GitHub - tmo1/sms-ie: SMS Import / Export is a simple Android app that imports and exports SMS and MMS messages, call logs, and contacts from and to JSON / NDJSON files. or, while proprietary, SMS Backup & Restore – SyncTech