Moving from Imac to mac mini 4

Then you need to fix that issue first. Find out why the Time Machine backups failed. Another option is to use either SuperDuper! or Carbon Copy Cloner (you can use the free evaluation versions) to clone the iMac's internal HD to an External Hard Disk and then use that instead of a Time Machine backup to restore to the new MacMini.

As you are working with a DAW, audio projects, you need to have active projects on internal drive to avoid any latency or other issues.

Personnally, my 2018 already had a 2TB ssd and as i also work some video, to me this has became a bare minimum.

With time, you will end with projects which can therefore be backed on external drive (and brought back as needed). But give yourself some space.

Obviously you want Cubase to be installed on internal ssd.

One more consideration : do you plan to use plug-ins on many tracks? Work with lots of audio tracks? Several plug/ins on same tracks? All consideration for more ram (32gb is a bare minimum - i have it on a 2018… I’d likely go for more nowadays. More important than paying for a cpu upgrade, since everything today is wear and throw and you can’t upgrade later.

Lastly: check compatibility for both Cubase 13, any plug ins and your Focusrite with macOS Sequoia, as many are not yet comoatible…. If an option, perhaps you may ask for the mac to come with Sonoma, although i doubt this is an option Apple will have, and going back by yourself may be a pain.

·       Always connect your old Mac's Time Machine External Hard Disk prior to startup, this will allow a migration from your TM backup and it will be dead simple! When you start the new Mac for the first time it will startup Setup Assistant (SA), SA will get to a point where it asks if you are migrating from another computer, select Yes and follow the on-screen prompts and it's done! It is that simple! This is the easiest, quickest and most reliable method to migrate from the old Mac to the new Mac is to simply connect the old Mac's Time Machine External Hard Disk to the new Mac using a USB cable before you turn on the new Mac. 

·       NOTE 1: You will likely need a USB A to USB C adapter, you can find them on Amazon for $10 or less.

·       NOTE 2: If you have already done SA on the new computer then simply connect the Time Machine External Hard Disk using a USB cable and launch Migration Assistant (MA) which is located in Applications - Utilities - MA. Then follow the on-screen prompts.

·       The ONLY difference between MA and SA is MA will create a new user account that you need to log into.

Both SA and MA migrate applications (not 32 bit apps), data files & settings. They do not migrate Mac OS itself. Some professional apps such as Adobe and Microsoft apps may require re-installing their apps as they will not allow them to be migrated. As long as you kept the security keys for installing their apps, it is not an issue. 

Finally, my recommendation is not using Wi-Fi when doing Setup Assistant or Migration Assistant. Why, it simply fails in a lot of the cases reported in these forums. A wired connection is more reliable and the last thing you need is a failed migration when there are safe methods readily available. Please read and follow the directions in Setup Assistant and Migration Assistant. If you do not have a Time Machine backup of the older Mac then create one!If you are not aware of Time Machine, please read Back up your Mac with Time Machine and finally if you need an External Hard Disk to use as a Time Machine External Hard Disk then many experience users on these forums prefer the OWC Mercury Elite Pro due to it's reasonable price, high level of quality and ease of use. 

Also, yes you can use an external SSD for startup however the wise thing to do is get the same (or more) amount of internal storage as your iMac. This will make your migration much smoother. Yes, you will pay more than the cost of a base MM but long after the money is spent you will be VERY glad you did!!!

❗️ – IMPORTANT – If upgrading from 10.14 Mojave or earlier, then your older 32-bit apps won’t work in any macOS since 10.15 Catalina! Those 32-bit apps and utilities must also be update or replaced.

Use this free utility> Go64 app from St. Claire Software to check your apps

The first thing you will want to do is run Go64 to determine which of your app and assorted utilities are 64-bit vs. 32-bit software. No macOS since 10.15 Catalina will run 32-bit software at all. You'll want to know which of your app will need to be upgraded or replaced.

After that, check with the publishers of all of your must-have software to make sure they have something that is compAtible with the newest macSO versions – Ventura, Sonoma and Sequoia.

After that, you can determine which Mac suits your needs best, but I will tell you all the newest Macs will run rinbgs around your old iMac.

The basic (£599) M4 mini will blow your iMac out of the water. You will wonder what is happening!

Yes, you can boot from an external drive and even if you use a dead cheap and slow (360 MB/s) USB 3.0 one you will not notice any reduction in performance.

That would point the finger at the External Hard Disk itself and not Time Machine or Mac OS. Get another External Hard Disk ( many experienced users on these forums prefer the OWC Mercury Elite Pro due to its reliability, reasonable cost, vendor support) over Walmart quality EHDs.