10 days too long for Rome? Heck no, not if you can fill your days with the many fabulous things she has to offer. We've stayed there for as long as a week - and not our first time - and still have things we've yet to see, and others we want to do again.
I'm not wild about doing "Tuscany" as a day trip, though, as It's very much a destination worth dedicating more time for. It's also not a singular place but a sizable region encompassing cities and towns (Florence, Lucca, Siena, Pistoia, Pisa, San Gimignano, Arezzo, etc. etc.) and countryside. Heck, I could easily spend 10 days just in Florence but it's rich in the sorts of things that interest me. Your interests might be different so you have to plan for you. :O)
It would be good to know how many nights you'll have on the ground in Italy? The suggestion to make a list of what you want to see and do is Rome is a good one; then you'll know if you do indeed have too little to fill your time. Do be cautious not to short-change her, though, by trying to cram too much into too few days just to try and fit in another destination. Rome is a city best enjoyed at strolling speed, with time to notice the details, for breaks now and again to watch the world go by, and to generally get to know her. You've also been given some good suggestions for other nice day trips you could take to make up for Tuscany: save THAT one for next time.
Pompeii: I would suggest getting there independently by train versus any of the vehicle tours (bus/van/car) from Rome just because it's a longer trip by road - 3.5 hours or so - than by rail (shave at least an hour off that, if not a bit more). If you think you'd like a human guide for the excavation itself, those can be hired at the entrance, or some of the folks on the forum here will have suggestions for good resources they've used. For instance this one (the 2-hour Pompeii Walk) comes up a lot; posters who've taken it have spoken highly of this tour, and it's very reasonably priced.
https://www.sharedtours.com