transferring files from a 2008 iMac to a new iMac

Click on the link to read how to...

Move your content to a new Mac - Transfer to a new Mac with Migration Assistant - Apple Support

Migration Assistant copies all of your files to your new Mac so that you don't have to copy your files manually. If your files are currently on a Windows PC, follow the PC migration steps instead. If your new Mac is using OS X Mountain Lion v10.8 or earlier, follow the Mountain Lion migration steps instead.

1. Backblaze will not work with Migration Assistant. Please make a Time Machine backup. Please read Back up your Mac with Time Machine. I suspect you are over thinking Time Machine. When you get an external HD to use as your Time Machine drive format it as Mac OS Extended (Journaled) in Disk Utility. Disk Utility is in Applications - Utilities - Disk Utility. If you do not know how to format a drive you can find many many YouTube videos that will show you how.
2. 32 bit apps will not run on current versions of Mac OS. This has been the case for many years now and I strongly suspect your Adobe apps are 32 bit apps so if you want to continue using Adobe applications you need to prepare to use their new subscription model or you should begin looking for applications that you can substitute. Prior to migrating you also need to find any third party apps you want to use on the new machine to find out which are 32 bit, you can do so by using https://roaringapps.com/collections/list-of-32-bit-macos-apps . If you have some third party 32 bit apps that need to be updated, please do this prior to migrating.

When you buy a new Mac 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. You will likely need a USB A to USB C adapter, you can find them on Amazon for $10 or less. 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.

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, never EVER use Wi-Fi when doing Setup Assistant or Migration Assistant. Why, it simply fails in most cases. 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. 

I'm starting to take notes for when I get a new iMac as my beloved 2009 is being left in the dust.

Thank you for your patience with my dumb questions:

1. I don't use an external Time Machine (could never get it to work consistently) but do backup through Backblaze. I think I understand that I don't need Time Machine and can use Migration Assistant, is this correct? Do I need to take my old Mac to an Apple store to migrate, or will the Macs talk to each other through Migration Assistant at home?
2. I'm using CS6 and have made copies of my InDesign docs as IDMLs to open on the new Mac. Do I need to save Illustrator, Photoshop, and Acrobat in some other version to be able to open, or will they open on a new iMac? My 2009 is using High Sierra 10.13.6.
3. Is there anything else I need to do to prepare for a new Mac?

Thanks very much

I have almost an identical situation. I'm transferring files from an old 2008 iMac to a "new" iMac 24" 8C CPU/8C GPU/16GB/2TB model that is still in its unopened box. I purchased it back in July, 2022 and have had it in climate-controlled storage ever since. We were out of the country and I'm about to open the box for the first time and make what, for me, is a major upgrade. I have always done TimeMachine backups, so I am glad to use the route recommended by you -- rkaufmann87 -- and greatly appreciate this approach. I also was wary of relying on the MA route utilizing the very unstable WiFi connection in our area. One additional question I have centers around the fact that I used to use another external HD (which failed) for my TimeMachine backups. I am currently exploring data recovery services to extract the files on that external 3TB Fantom Drive (a Seagate Barracuda). According to messages from my attempts to repair/rescue that failed HD, I can "open or copy files on the disk, but can't save changes to the files on the disk." I wondered if my OLD TimeMachine backups -- if I can gain access to them -- will allow me to restore the thousands of photos I have lost? However, if I follow the advice to migrate my data from the NEW sets of TimeMachine backup (on a 6TB SSD which operates perfectly well) to my "new" 2022 iMac, will that strategy permit me to then restore my photo folders which were backed up to my OLD sets of TimeMachine sets? I hope that makes sense. My only chance of restoring all those photos is to rely on the OLD TimeMachine backups, which -- sadly -- are currently not accessible due to that Fantom drives failure! I just did not know if I can "mix" these two different backup sets, in attempting to later restore specific folders from a specific date (focusing on just those photo folders from the past). I do not use iCloud as I do not want my digital paintings to be "managed" offsite. I have had horrible experiences in the past, losing files that I had relied on web-hosting servers to archive and preserve. Now they are gone forever.