If you are dead set on buying a complete rifle, I would highly recommend you getting folding front & rear back up iron sights.
The benefit of folding sights is that when they are down, they are out of the way and you don't have to worry about them snagging, catching, getting clogged or otherwise encumbered.
If your optics, whatever they are, should fail, you pull them and hit a couple of buttons and you are back in the fight.
Co-Witness is something that a lot of people like in their AR platforms. This is when your sight point of your iron sights are exactly in line with the red dot or reticle of your optics. And that is a very good idea, but for me personally, I like one or the other, not both.
When you have three points of a sight picture, a bump or knock on one can affect accuracy. Should the scope get whacked, you probably know it happened.
My recommendation would be to get a set of quality folding sights like those from Yankee Hill Machine or some place like that.
Good luck and keep us informed of your progress.