Exciting! We did USH on a Sunday in July, so I was expecting crazy crowds, but it really wasn't bad. Here are my thoughts.
1. Pay for the early entry into Super Mario World.
2. If you pay for early entry, you need to be towards the FRONT of early entry to make it worth it. Our Lyft dropped us off at 6:17 for a 7 AM early entry opening, and there were already three families lined up behind each turnstile. Do not arrive any later than 45 min before early entry. We didn't run; other people did, so we were far from the first group into the land, but we still walked right onto the Mario Kart ride at 6:56 AM. We got off the ride, and the posted wait was only 30 minutes, but we skipped a re-ride in favor of playing the games and meeting the characters before wait times grew.
3. My kids are 6 & 9, and we only bought one Power Up band. My 6 year old was more interested in meeting characters and my 9 year old wanted to play the games, so my husband and I divided and conquered. My 9 year old played all 3 games before 8 AM. The games are fine, but the whole reason to play them (I learned from a dad in line, it's not well advertised) is to get 3 keys (you get a key for winning each game) and the 3 keys will get you into Bowser Jr's castle for the bonus game. The bonus game makes the entire thing worth it. I didn't do it, because my 6 year old wanted to rope drop Harry Potter land, and I took her there, but my husband took my 9 year old into the game, and he said it was literally like stepping into a video game. It was really really cool.
4. By the time my husband and son finished the Bowser Jr game, it was about 8:30. At that point, they left the land because they said it was insanely crowded. We enjoyed the rest of the park, which was completely empty compared to SMW, until about noon when we decided to take a break. We came back around 4:30 that afternoon to re-ride a few favorites. Lines were pretty short by that time.
5. Maybe it's because we went on a Sunday, but by 5 PM, the line for the Mario Kart ride was only 90 minutes (it had been over 300 during the day), so my recommendation would be to get up early and do what you can in the first hour, and then maybe revisit (if you want to) during the last hour of operation.
I hope this helps! I was really nervous about our day at USH, because I was a total newbie, and I thought visiting on a Sunday in summer could be a disaster, but we had a really nice time. Good luck!