I’m planning installation of Scale on a Terra-Master F6-424 with 6x12TB, 16GB ram and two internal m.2 ssds. All my hardware arrives Saturday, except for the storage which is another week out. I’ll be setting up a media server, running VMs, etc.
So, install RC or stable? Do I need to wait for the spinning disks or can I install the OS and start tweaking the Linux environment to my liking?
Very excited!
Welcome 
I’d go with stable unless you need a feature provided by RC.
I personally wait for a while before I update to shiny new releases.
And yes, you can install it and add the storage later. You do not create any pools during installation anyway.
Truenas is an appliance os, what do you want to tweak? Most of the underlying Linux environment is either locked down or must be managed through the truenas gui.
Tweaks: For a new linux , I install ssh keys, my favorite editor, various command-line tools, etc.
I am afraid you should not do any of that.
TrueNAS is not a full blown distro. It is an appliance.
You can install what you want by enabling developer mode but it is definitely not recommendes.
These two statements are likely going to be contradictory. 16GB RAM is not very much, depending on the VMs you plan to run. Remember that each VM needs some RAM and you may be short.
How do you know if you are short? An easy way is to look at the SWAP file usage. Anything (in my opinion) above a few KB (for argument 50KB) means you have run out of RAM. Ideally you should never have a value above 0KB for swap file usage.
So take a look at that once you build up your system and start to add your VMs. I suspect you will be doubling the RAM to 32GB but maybe you will be lucky and squeak on through this.
What hard drives are you buying?
Otherwise it looks like a nice build, however to point out a few things so you are aware:
My VMs are debian instances (2gb each x2), currently running on an old 8gb linux laptop. The drives are 6 12Tb IronWolf. Doubling the RAM will happen, but not initially.
Personally I don’t like the Terramaster software and think that TrueNAS is better.
Order a 32GB DIMM now - you WILL need it.
I have read that a rule-of-thumb for planning is 1GB of ARC per TB of data, but IMO that is likely to be a lot on the high side - and in any case it will depend on your usage patterns. I have only c. 3GB of ARC for approx 10TB of data and I still get a 99.5%+ ARC hit rate.
I hope you are planning a RAIDZ2 pool on your 6x12TB disks.
I would use one (small) m.2 SSD as your boot drive, and use the other (larger) one as a pool for apps and VMs (with replication to the HDD pool as a local backup).
In terms of VMs and Apps, max 32GB of memory will allow quite a few apps and / or few VMs. You will need to plan your memory usage if you start to use VMs.
As for whether to start with EE RC or Dragonfish, since you are fully populating your drive slots, you will not need that RAIDZ expension capability. So the choice of EE or Dragonfish will come down to apps.
At this stage so close to full release of EE, I would personally go with the EE RC and avoid a later app migration (from Kubernetes to Docker apps). But do be prepared for the possibility of encountering an EE bug or two.
16GB will probably be fine with 4GB of VMs.
I regularly run a 16GB truenas VM on a 32G TrueNAS instance, and in that 16G VM I run an 8G TrueNAS instance 
(I use it for testing nested virtualization!)
I work on the basis that 8GB is required for TrueNAS and then I have 8GB for VMs.
I just ordered 32gb of RAM. I’m leaning towards RAIDZ2, 24TB towards parity still leaves me with triple the storage of my current primary NAS.
