Our tentative Itinerary for Sicily....your advice would be appreciated

I would flip Agrigento to get an early start on the temples and visit the museum in the afternoon. The site is vast, but there is a golf cart that will take you to three or four points for a few euro. You could take it to the highest point and walk more or less downhill the rest of the way (although the site is not steep).

You can get to all the places you listed by bus and/or train, but getting to the Villa Romana del Casale will be a challenge, the minibus only makes one or two round-trips per day from Piazza Armerina.

I would go to Cefalu rather than Mondello, but check to see if the work in the cathedral mosaics is done.

It would be more convenient to sleep in Trapani rather than Erice for your trips to Marsala, Segesta and Erice.

Not sure you can get to Agrigento and Selinunte in one day, plus going to Agrigento first means a long backtracking trip to Selinunte (which also has a tram to get you through the six kilometers of the Archeological zone.

You can take the bus or train from Taormina to Catania Centrale and then take the Alibus to the airport, if there is no direct Alibus from Taormina.

Overall, I think you are not realizing how long it can take to get from A to B. Use Rome2Rio.com for some time estimates.

Don't forget to consider buses as a viable mode of transport. There are many routes where buses are the preferred method of transport over trains (for example, getting to Taormina and from Taormina back to Catania airport). I would look at each link carefully with a guidebook (Lonely Planet is decent) and not write off the bus system. Just be aware that both bus and train schedules really suffer on Sundays.

The train doesn't go to Erice. You get to Erice from Trapani, via bus or funicular. Or a taxi, of course.

You can get to Monreale by public bus, so you don't necessarily need to spend the money on a tour unless the tour includes an additional destination you're interested in.

You're skipping Siracusa and the Baroque towns in the southeast, but you can't do everything in 11 days. I can't resist pointing out, however, that Taormina is quite small. And very, very touristy. For me, three days would be two days too many. But it is undeniably beautiful.

There's limited rail service in Sicily, so buses are often useful if not essential . Be aware that there is very little bus service between towns on Sundays and holidays. Be very, very cautious about planning to go to a different city on a Sunday.

Have you checked out RS Sicily Tour Itinerary to see where they go? His tour itineraries are always a good source of information when planning a trip in Europe.

Have u considered a guided tour? I have just returned from A 9'day tour which included much of what your interests are. You can always add additional time in Palermo on the front side. Public transit in sicily is not as easy as other parts of Italy. We took Gate 1 tours. I too am a seasoned independent traveler but this time a tour was the best option.

I would stick to the independent trip idea, there's no evidence that you need to take a tour unless the transport piece is somehow untenable. Sicily is very easy to travel in independently if you are flexible and can "go with the flow". And public transit is not hard at all (I think that's an impression that people have but I'm to sure where it comes from...it's true that there are no high-speed spiffy trains in the southeast where I went, but that's not a deal breaker). It looks like you have a decent plan and you've really thought it through..now you just have to fit it to your transportation logistics and make some needed tweaks.

Depending on transport connections and schedules, I would recommend some flexibility in trading off where to sleep (for example, Trapani over Erice, if it's easier to get to the next site directly from Trapani. Erice is just a cable ride or bus ride from Trapani). If there are no direct connections from Argigento to Piazza Armerina, you may need to consider an alternative: Catania may make a better base to Piazza Armerina, as the connections from the airport to various towns are very good. Or perhaps you can go on a guided trip to some sites which are not as easily accessible by bus or train (example, Mount Etna).