Just an update
I bought a thunderbolt 3 doc that connects 2015 iMac (TB2) and the external NVMe drive (TB3). It works great. BlackMagic rates it around 1200 MB/s. So it is more responsive than the internal SSD drive.
https://www.amazon.de/-/en/Thunderbolt-Docking-Station-Laptops-Ethernet-gray/dp/B09PY37TVZ/ref
The enclosure will typically come with a USB C-C cable (2019 Mac) and a USB C-A cable (2015 Mac). Like this one.
Depending on how serious you are on the matter, there's specifically made luggage for 24" iMacs that are encased in hard plastic. They're pricey, but if its something you'll use frequently its probably worth the investment.
Reminds me of the old Mac Classic luggage days. Ah, memories.
> I’m just looking for suggestions on external Hard Drives & usb hubs.
Hard Disk Drives (HDD) are spinning drives, and very slow, but generally reliable; so they are good if you want to store a lot of data, because they are cheaper than SSDs, and you likely don't need to access that data often.
SSDs are very fast, but generally more expensive. That being said, you can get a 1TB SSD for $129.99 on sale today it seems. I'm a big fan of the SanDisk Extreme Portable SSD; I have 4 of them. Knowing nothing specific about your needs, I recommend this because it better matches the speed of your iMac's SSD. And 1TB is usually the right amount for most people.