[Tinwarble]

 Should I turn the sleep timer off?  I have just set up the Nvidia Pro and run it through my theater center.  My remote is a Logitec Harmony One.  With my prior media center, I let the computer run all the time.  Should I do the same with the Nvidia.

That's up to you. If you don't want the Shield to go to sleep when idle, then yes. Or you can change the time it's in idle before it goes to sleep.

Right now it turns off by itself after a bit and for some reason also turns off the TV when it does.

Turn off CEC, if you don't want this to happen.

Also, should I update to Leia or wait for it to be final.  I am using 17.6 and I thought the integration from 18 might be nice. 

Again, up to you. I use v18 as my daily driver on all my Shields and find it pretty stable. But depending on what you use Kodi for you may find it the same or less stable. The only way to know is to install it and try it.