Do I need 16gb of ram for the M1 Mac Mini?

Order it with 16GB RAM. I did. As time passes, neither macOS, nor third-party applications are requiring less resources, and having 16GB RAM eliminates short to mid-term RAM insufficiency. One can neither upgrade the RAM, nor the internal storage of the M1 devices, so best to do it right at time of purchase.

Check out some of the YouTube videos on the difference between 8GB and 16GBs of RAM. For most there was no performance improvement with 16GBs over 8GBs.

That being said, if your machine needs to use swap memory to do a lot of tasks... it will use your SSD drive to write swap to. Just like every computer on the planet writes swap to the local hard drive. Typically it uses swap to free up memory, so the more memory you have, in theory, means less use of swap.

SSD drives perform poorly when full or nearly full. They also don't like excessive writes as that will wear them down. Of course it takes a long time to wear out an SSD drive, but if your drive is small or nearly full, it can speed up the process of water down. Since the SSD is not replaceable, you will want to protect it by giving it the most room to work with (up the size) and more memory (up the RAM) to reduce swap file writes.

If you really don't have any heavy loads... most people don't, it's not as much of an issue.

So the performance boost from either upgrades is likely to be seen over time for most... much like the cost savings of a new roof or insulated windows is calculated out over years versus immediate savings.

FWIW, I just went through a one hour photo editing session where I was

developing Nikon RAW files and tweaking the resulting TIFF files.

The apps used were open all the time: Affinity Photo (M1 optimized),

Adobe Bridge 2021 (Intel) and DxO PhotoLab4 (Intel). The process was smooth

and very fast, a minimum of twice as fast doing the same on my late 2013

27" iMac with the Intel apps and Affinity Photo blew away my iMac.

All of this was done on my new M1 MacBook Air (8 CPU/8 GPU)

with only 8 GB of RAM with no lag moving images back and forth through

this process. It did take some time initially opening the Intel apps (translation?)

but really not any longer than on my iMac (also has SSD).

So, my guess is that unless you do work on data files that are

very large (2-3 GB+), 8 GB of RAM may be plenty.

However, if you were using Photoshop + Lightroom for the same

process, being the memory pigs they are, you would need 16 GB.

Higher RAM the better the performance.

**If I do change my mind can I upgrade at an apple store later?

No you can't purchase a RAM upgrade for M1 Macs since its already built-in.