Loire Chateaux - Advance Tickets?

Every château will have different ticket/entry criteria so you need to check the official website for any château you may want to visit to see if pre-purchased tickets are required. I tend to doubt they are but they may be offered anyway. But, you are unlikely to find any info on any château website about how many people they allow per day. Of all the châteaux you mentioned the one that is likely to be the most crowded and where you might want to buy a timed entry ticket is Chenonceau. On their website they recommend buying a ticket for a time slot to avoid standing in any potential line but it doesn't specifically state that it is necessary to do so.

https://www.chenonceau.com/en/

https://chateaudechenonceau.tickeasy.com/en-GB/home

There may be combo passes to give reduced entry prices for multiple châteaux but be careful to avoid 3rd party vendors (Viator, getyourguide, etc.) selling such passes and instead check official French tourist office websites or other French government websites. There are also various blogs not selling passes that will point you in the right direction. In a brief google search I came up with a couple of websites you can check but I did no research myself so I'll leave that up to you.

https://www.touraineloirevalley.co.uk/plan-your-holidays/practical-information/passes-and-reduced-fees/

https://francetravelplanner.com/go/loire/discount_tix.html

Merci Mystique,

Vous m'a dit ce que je pensais et vous avez raison de Chenonceau.

Bonne route à vélo. ;)

And since you can read/write/speak French then you are likely aware that the French versions of websites are always more thorough and have more/better info than their English language counterparts.

Peut-être, mais je sais seulement assez d'etre dangereuse.

Don't but tickets from third party vendors for chateaux.

When you're travelling it could be very busy (you don't give precise dates). Last year during a couple of the May long weekends Chenonceau was so busy that they put up the "full" signs and weren't letting anyone else in. Unfortunately, tickets from third parties (even tourist offices, etc) don't give you access to booking an entry time, so although you would have got into the grounds, you wouldn't have got into the house. The others you should be OK on the day.

Buy from the Chenonceau website and time your entry for about 45 minutes after you plan to arrive