Passwords: Your machine has something called a Keychain which stores all your password etc. Make sure that Keychain is synced to iCloud (you will need to go into the iCloud options on your old machine). iCloud will sync paswords via the Keychain. Keychain management is now managed through an Apple app called Passwords, so you can simply ensure that you go to the iCloud options in Settings and ensure that Keychain is checked to be stored in the cloud, so that when you bring up the new machine, the keychain will be copied to the new machine and can then managed through Apples separate keychain manager, Passwords. You will not need 1 Password unless you have other non Apple machines across you wish to sync password.
Firefox has the ability to sync bookmarks and password across all instances of Firefox. Make sure you have an account with Firefox and then sync the current instance of Firefox. Then when you install a new instance on your new machine, Firefox will sync up bookmarks and passwords,
If you to want to copy over the applications you will have to use Migration Assistant, but be aware that often the new copy will need your account info for those apps that were purchased and have keys. MA will not necessarily copy all the information for apps that have a sign in credential requirement. You are much better off reinstalling and signing in again e.g. for MS 365.
For your photos, what application do you use to manage them? If it is Photos then they are stored in a proprietary database format (Photo Library) which will need to be copied over complete. When you start Photos, hold down the option key and point it to the location for the library, If they are not managed by an application, then you can copy them over and point the app to them, but Lightroom for example has a catalog that knows where the photos are and you will loose all the information related to editing. You will need to look up how to migrate a Lightroom library. It is not easy.
As far as I know, Apple Mail requires that all mail be stored in the cloud, so if you have Apple Mail managing emails from your own self hosted options, you will probably find it has moved all of them to the cloud, but that would take up space and I am not sure I understand whether you have paid to get more iCloud storage or not. I would need more info to help how this might work on your new machine. The mail client dictates the requirements, and few if any these days work with mails stored locally only (they may have the ability to store a copy locally, but always work on the cloud stored emails.
Carbon Copy Cloner (CCC) and Migrations Assistant (MA) are rather different in what they do and the facilities you are provided. CCC will clone a disk at a very low level so it can be copied to a new disk but I do not think that it is appropriate. However it will also copy specific files and folders to a new location either as a backup or straight copy. From what you have said CCC may not be appropriate here unless you have identifiable folders on your old machine which you want copying to your new machine. MA will clone the system from your old machine to your new machine, but it knows what needs to be copied and what does not, so it will only copy the system files it needs and settings along with user data. It is the safest option unless you want to customize what data you want copied or want it placed in different place on the new machine. Note that if you are using Photos, the library will be copied. If you are simply storing the photos as date, it will copy the photos as user data. Note my comments about Photo managers like Lightroom since the have a relationship between the location of the photos and the information regarding any changes you have made (assuming the editor in the photo manager does none destructive editing: they keep a copy of the original and then have a list of the changes you made which is applied when you open the photo.).
If you use MA, the new machine will have the same name as the old machine. You can change the name of either machine. If you want to keep the old machine intact, then simply change the name of the new machine in the Settings> General>About option.
I think you are best using MA based on your requirements and concerns and then sort out passwords and app credentials after everything has been migratated. However it will bring everything over that it can, although your old machine has a much older OS and so may have some things it cannot copy. Once the migration is done, you can an app called Clean My Mac (available on the App Store) to remove any orphaned install components or config files and remnants that are not required.
I hope this makes sense and feel free to ask more questions.
