We stayed at Hotel Genio, 1-minute walk to Piazza Navona. On the first afternoon, we walked to the river to see Justice building, and St Peter's Basilica, continued to Spanish Steps, Trevi Fountain, Pantheon, and Piazza Navona.
Next day we walked to Castel Sant' Angelo, St Peter's Basilica, and Vatican Museum. We bought tickets for the before public small group tour at 7:30am (open at 8:30a to the public). For 2 hrs the lady guide took us slowly and explained in detail. There's no talking, no taking pic/videos in the Sistine Chapel, so she explained to us before hand. Then we had 25-minutes inside Sistine Chapel, quietly enjoy everything in awe. After that she took us on way to the gift shop to finish the 2hr tour. We continued with breakfast inside the Vatican Museum. As we got out, there was a long line of people waiting to buy tickets (they could've bought online).
We then took uber to the Colosseum. We had bought tickets for the underground tour of the arena (and upper). After that we went to the (nearby) Forum Forum and Pallatine. Lots of walking, >30,000 steps that day. But saw so much.