Hey Bob,
Regarding your storage solution, if you can’t use your current raid id suggest upgrading that at the same time as your machine.
For some context, I run a MacMini M1 with 8gb Ram, I edit 4k, and do some color work. I have always been impressed by what this little cheap Mac can handle. Apple Silicon is a game changer for me with working with media, you will be surprised how little you’ll need to do your work. Black Magic has optimized Resolve to work very efficiently on the new chip set.
Storage suggestion, I use an external 2TB SSD MVNe drive to edit off, and then have a cheap desktop external drive Seagate 16TB to manage my files (I have additional drives for Backup). I only load the current project onto the 2TB SSD so that I have enough space. Obviously if you have bigger projects you should get a bigger drive. If you can afford get an external TB3/4 ssd, but it must be an MVNe drive so that is fast enough to handle multi 4K steams if necessary.
Raid is good if you can afford it and you have very big projects, but not necessary in my view if you are doing HD work and even 4k work.
I agree with Paul, buy the best you can afford at the time as it will give you the longest life span. Also remember the ram issue, you can’t upgrade it later. so get more than you think you need.