Amboise

Crowds will be very high, so yes, have advance purchase tickets for Versailles. And get there well before the gates open unless you want to be stuck in a very long line at security.

You can just buy your tickets when you arrive for the sites in Amboise.

You will not need a ticket to the castles near Amboise. We had a rental car and loved seeing the beautiful countryside as we drove from one to the other. DO NOT MISS VILLANDRY! It’s gardens are a feast for the eyes! Make certain you notice the lovely fresh flower arrangements in the castle of Chenencou........the ladies there put new flowers in on a regular basis and they are incredible. We were charmed by Amboise and loved walking through the town each morning after we ate a delicious pastry at one of its shops....it was also a lovely quiet town to relax in each night for dinner after touring the countryside. We stayed at Le Manior les Minimes........a beautiful old home that had been restored to serve as a hotel. The sweet little chapel on the grounds of the Castle of Amboise makes a lovely backdrop for pictures. Amboise will always be a favorite memory for us!

PS.......toured Versailles and loved it.......we were at a disadvantage in that we were there in late July with a sea of humanity and the castle was SO CROWDED......(watch your pockets for wandering hands in the crowds!) and try your best to get a ticket that will get you in past the crowds......I think I remember that we had a Paris Museum pass and thought it would get us past the HUGE LINE but it did not and we had to wait despite thinking we would be at an advantage!

You can purchase tickets for Versailles in advance and avoid the ticket lines. You´ll want to be at the security line as early as possible because the crowds are horrendous.

Versailles is really not on the way to the Loire Valley and stopping there means you will probably arrive Amboise very late in the day; possibly too late to see much. Château d´Amboise is best viewed from the far side of the Loire River. Given what is otherwise available in the immediate region, I would not waste time going inside. Chambord, Chenonceau, Cheverny and possible Château Blois are all much more compelling visits. These are the places you should concentrate on; Villandry has a wonderful garden but you´ll need a lot more time to include it as it is some distance from Amboise and traffic around Tours during rush hour can be difficult.

Versailles can take most of a day. The drive to Amboise isn't too bad but expect to be fairly tired when you arrive.

Advance tickets aren't mandatory. If it's a nice day in early September, however, it's probably optimal to arrive at Versailles with pre-purchased tickets at least 30 minutes before opening. You will have to go through security, so leaving any large bags in the trunk of the car will save you having to check and recover your bag (I had to check a full size umbrella, but a fold up one would have been okay).

We went straight to the main thing, the mirrored hall, then the garden and petite palaces, then decided we were too worn out to go back for more of the main palace.

The Loire Chateaux are different. I never saw a big line at even the most popular of the Chateaux. Purchase your ticket when you arrive and you will be fine. No need to arrive early either. There will be plenty of people but they drift in and out all day.

In one day (with a rental car) from Amboise, you can probably see Chenonceau, Amboise and Clos Luce. I did it with a bicycle. The only problem I had was missing most of the gardens at Clos Luce because there were more than I had time for. I think you should visit Chenonceau, it seems to be everyone's favorite (including mine).

The one thing I'd do in advance is use Google maps and click on each place you are interested in. The left part of the screen (scroll down) will have the current open hours. Make sure you know the hours, opening, closing and what day they are closed, before you start out.