Sure! I'll provide the useful tips for your travel plan to Tokushima, Kochi, Ehime, and Kagawa.

Best Time to Visit:
The most favorable time to visit these areas would be in spring (March - May) when cherry blossoms bloom, and autumn (October - November) when leaves turn into beautiful autumn colors.

Route and Accessibility:
You can start your journey from Tokushima, reachable by flight from Tokyo or train or ferry from several major cities. Kochi and Ehime are accessible by train or bus, with Kagawa being the most accessible, with high-speed rail links from Osaka and Hiroshima.

Altitude and Acclimatization:
The altitude variation isn't much of a concern here, as most of these places are at sea level.

Accommodation and Booking:
From luxury hotels to traditional ryokans, you'll find a range of accommodations. In the peak season, prior reservation is recommended.

Clothing and Essentials:
Pack according to the season of your travel. Lightweight clothing is advisable for the summer months, with a jacket for cooler evenings. Winter requires warmer clothing.

Health and Safety:
Medical facilities are up to the mark in these cities. Still, it's always good to carry your medicines and first-aid kit. Take precautions against sunburn and dehydration and remember to wash your hands regularly to prevent any kind of infectious diseases.

Local Etiquette and Respect:
Japanese society is known for its politeness, humility, and respect. It's polite to bow when meeting someone. Try to speak softly and avoid being too noisy. Take off your shoes when entering someone’s home, or areas having Tatami floors.

Remember to enjoy the local cuisine while respecting the cultural norms of these beautiful prefectures!