2tb drives seem a bit small to me. but if the raidz1 pool of 3x 2tb drives is enough storage for you, then that should be fine.
but in terms of the best bang for buck 4tbx3 or 4? i’m using the later. Not saying you have to go similarly, but that is sufficient for most people. Only pay for what you actually use.
If you are looking for more zfs tuning videos, lawrence has a bunch of them you can check out
Since you are new to truenas you may want to check out how to setup the smb and acls for your truenas. lawrence explains it well here
are you using core or scale?
If you plan to use apps, scale is better. Core is very stable, but scale is also being pushed to enterprise good sign that it’s stable enough for production use for a while now. I’m on dragonfish which is considered beta and not for production.
make sure you have monthly raid scrubs once a month set if they haven’t already.
your ssd is already being used for your boot pool? not sure what other optimization you want for it. You could go for a mirror boot pool ssd if you want, or just stick to your current setup. That’s about it?
In Tim’s video he explains the other options. lots of it is optional. You don’t really have to do all that, i didn’t. I just deployed the basic truenas setup and it just works fine 
but if you want to explore the extra features just check lawrence, tim or some other youtuber explaining those stuff.
Guess you are set on your backup and restore for your desktop pc? so i won’t go into that 