I bought my F in Southern California in August 2018 and I had about 150 hours or so total time. This was about 5 months after returning to flying after a long hiatus. I flew commercial to Southern California, finalized the purchase and then the previous owner flew us up to San Jose where I did my transition training which was two full days. He flew back commercial. At the end of the 2nd day, I flew solo for the first time in the Mooney to Stockton. I was concerned about the marine layer near the coast and without an instrument rating, wanted to maximize the chances of leaving early the next day. The Stockton area was having clear mornings so that was my logic. The next day I flew 6.5 hours total over I80 essentially with a stop midway in Ogden, UT until hitting Scottsbluff, NE where I spent the night. Flew another 5 hours to Wisconsin the following day, again with a midway stop in Lemar, IA. I'm still a low time pilot but some tips that helped me:
-Fly early in the day
-Fly a route over an interstate - those are the lowest points over mountains and might provide a landing spot in an emergency if no airport is available.
-I was prepared to not fly if forecast winds 1000ft over peaks in the Rockies were more than 20 knots - my understanding is that a mountain wave is less likely to be an issue if wind speed is lower than that. Just a rule of thumb and not sure if its backed by evidence.
-Don't wait until 12,500 to use oxygen, for reasons others have already mentioned
-Assume you'll have to stop earlier than you planned somewhere along your route due to weather. If you don't, then thats a bonus. I was anticipating having to leave the plane somewhere and then returning another week. Fortunately, I had good weather for the most part...had to avoid some broken layers/clouds a few times but that wasn't a problem between ATC using flight following and Foreflight ADS-B In
-My plane came with portable oxygen, portable radio, and previous owner gave me extra emergency food packs/tools/bottled water/space blanket and things I might need if I had a forced off field landing...even a little stove!
-I intentionally flew conservatively regarding fuel consumption because the plane was new to me and didn't yet have a method of getting accurate fuel flow at that time (or estimating it), other than the previous owner's experience
-Using a porta-john is much harder in flight than I thought it would be LOL!