Multiple Monitors Not Working/Slow Startup

Can't get multiple monitors to work in Sierra on Mac Pro (2013). I've tried all the usuals like restarting, PRAM, etc. with no results. I have a TB Cinema Display and two Dell 23" via mini display port/VGA adapters. They will all work individually, but not at the same time. The Mac does not recognize the monitor unless attached at boot up (ie: not hot swappable). Just to note, I also have a TB HD attached and two printers via USB. I've disconnected them to see if they were the issue and same result.

Also, it takes several minutes to boot up and I get some weird artifacts on the screen during the process.

As a side note, I've also installed Sierra on our media machine Mac Mini (2011). Runs fine with no problems and has a 20" Samsung monitor and Samsung flatscreen TV attached.

I appreciate that we no longer have to pay for the OS, but quality control has gone to complete (bleep).

Going back to El Capitan.