Sure, I'd be happy to help you with some travel tips for your trip to Nantes, Angers, Le Mans, and Tours. These are wonderful cities in France with so much to offer.

Best Time to Visit:
The best time to visit these cities would be from late spring to early autumn, specifically from May to October, when the weather is pleasantly warm and there are numerous local festivals.

Route and Accessibility:
These cities are well connected by the French train network, it makes a convenient and enjoyable itinerary. Starting from Nantes, you can take a train to Angers, then to Le Mans, and finally to Tours. Renting a car is also a great option if you prefer to drive.

Altitude and Acclimatization:
These cities are not at a significant altitude, so you should not have problems with acclimatization.

Accommodation and Booking:
There are various types of accommodations available in these cities to suit every budget, from luxury hotels to budget accommodations. It's always recommended to book your accommodations in advance to secure a good deal.

Clothing and Essentials:
Since the weather can be somewhat changeable, it's best to dress in layers. Don't forget comfortable footwear for city walks, "comfort is key". Also, an umbrella or lightweight rain jacket is recommended.

Health and Safety:
All of these cities are relatively safe but like any place, always keep an eye on your belongings. French healthcare is excellent but make sure you have travel insurance.

Local Etiquette and Respect:
French people appreciate when visitors make an effort to speak a bit of French. Also, it's customary to say 'bonjour' (hello) when you enter a shop and 'au revoir' (goodbye) as you leave. During dining, keep your hands on the table (but not your elbows). If you're invited to someone's home, bring a gift such as wine or flowers.
Remember to show respect for the local culture and traditions.