First of all, congrats!
Check if the box seems sealed, the tv itself has plastic stickers all across the bezels, and behind also. The installer will ask you if he should remove the stickers, I preferred to do it myself (feel this 50% of the fun of buying new tech
)
I used this thread for getting the panel usage info by going into service menu. Mine was 0 indicating it was a new box piece:
How to Check your Sony Bravia Panel Usage Hours From Remote Press Display (I+) 5 Volume - Power Gets you into the diagnostics screen which shows the hours. The bottom left 5 numbers are the hours Next 5 are boot count and last 5 are the lcd panel hours.
www.hifivision.com
Apart from that open YouTube and check for Dirty screen effect, colour banding and they will help you check for dirty panel or any abnormal banding, issues with back lighting etc. If the above 2 tests are fine then you're good and we get into the good stuff.
Use
https://www.rtings.com/tv/reviews/sony/x900h/settings for doing picture calibration. Videos available for the same on YouTube as well if you prefer video.
Post all this, enjoy!