Let me just say that Im a very new unraid user, and I too have moved from Truenas. I and quite happy with the move. So far, I've had very few permission issues unlike truenas where i was always troubleshooting how to get things to work in truenas. The plugins/apps seem to install flawlessly. Im currently using RSYNC to migrate all of my data over to Unraid. Should take about 6 days to fully transfer everything. Regarding your apps, there seems to be a buttload more apps being offered in the app store. Try it out for 30days for free.
You may want to pick up 1 extra drive for "parity." read up on parity if youre not familiar with it.
unlike Truenas, there's a cool file manager that you can download from the apps store (krusader) Yes, you can drag and drop from your Truenas in Krusader to unradi. However, I easily max out my 1 gig connection with rsync.
SpaceInvader one has some awesome tutorials.
Here's on on Parity: