Should I get an SSD to boot Sonoma to my 2019 27" iMac?

Without reciting 9 months of painful problems after upgrading my Retina 5k, 27 inch, 2019 iMac (currently 16 GB RAM and 2 TB storage memory) to Sonoma, at Apple's suggestion I have reverted to Ventura. At least part of the problem, which no one will say out loud, seems to be the Fusion Drive in the iMac. My iMac again seems fine, which it was before Sonoma. However, I cannot do a Time Machine restore of backups for the last 9 months when Sonoma was installed, which means I cannot access years of Mail folders that I really need. To allow that restoration, a senior Apple tech advisor and some third parties have suggested I by-pass the Fusion Drive by buying an SSD, installing Sonoma, and making the SSD the boot drive. The alternative seems to be to buy a new $$$$ iMac and give up my cherished 27" display (the largest display is now 24" instead of 27" - ggrrrr!!).

That brings me to my questions (I am not a techie - hopefully some of you are!):

1. I have read enough posts about people having problems with SSDs so I wonder if this solution is advisable (frying pan to the fire?).

2. Does the SSD completely replace my iMac drives so that I lose access to its 2 TB storage memory (in other words, is it like a completely new computer, but using my iMac display)?

3. With new iMacs, Apple talks of "unified memory" instead of RAM. What does the SSD do for RAM, and do I have to watch RAM specs for purposes of my large iMovie projects?

4. I have a partitioned Seagate 8 TB drive that I used for Time Machine backup (4TB) and file storage - mostly video/photo storage (4TB), which is connected via USB-A. Can I still use the Seagate for these purposes? If so, do I need a hub?

5. Will Time Machine backup whatever is on the SSD to the Seagate partition for Time Machine?

6. If I format the SSD as Mac OS Extended (journaled), will Searchlight be able to search it (I don't need to be able to use Windows files).

7. Are there other issues of which I need to be aware?

Thanks!