I was there last summer with Princess Cruises. The buses are modern air conditioned buses, though sometimes the heat may be more than the AC can keep up with. They usually do not have bathrooms. The trip is only 90 minutes, so that shouldn't be a problem.
As for tours, you can't see Rome in 1 day. Pick whether you are more interested in ancient history or church history. If ancient history interests you more, choose the Pantanon, etc... If church history is more your interest, visit the Vatican. If you've been to Rome before like we had, then sign up for Rome on your own tour. You'll have bus transportation back and forth & some direction. When you arive, they will tell you what time to meet the bus in the afternoon and pick you up then.
Rome is full of professional pickpockets, even groups of kids who will try and take your wallets & purses. Be very careful!!!
No matter what you do, you'll enjoy Rome.