I like it. I have an OR also and it has been literally flawless in performance for about 4,000 rounds. I also run the PA red dot you have. Great choice.
I'd change (or I did change) the stock to either the MOE or STR. Great cheek weld with both and a great feel. I'd also go with (I did go with) the MOE grip as well. I've tried a couple and always come back to this one.
Backup sights are nice if you run your battery down at the range but if you are using this for any kind of defensive carbine, then yes, backup sights are a good idea. Sling also and a light.
Have fun with it!