I went with only one grate, 7-8" height. I have never tried a big turkey before, but that is probably about the only thing that might not fit. I think you are fine. If you find that your bottom grate cooks too hot, add a deflector plate or water pan before it. Benefit of a UDS, it is never a complete project, you can always do more.
Traeger Texas, UDSx2, Weber 22.5" OTS, Weber 26.5" OTG, Weber Performer Platinum Blue