Absolutely, I'd be glad to help with your travel plans to Mildura, Renmark, Echuca, and Adelaide. Here are some tips:

Best Time to Visit:
The best time to visit these locations in Australia is during the spring (September - November) or autumn (March - May), where the weather is most pleasant. Summers can be very hot while winters are generally mild.

Route and Accessibility:
Your journey can start in Adelaide, then travel to Mildura, Renmark, and then to Echuca. All these places are well connected by road.

Altitude and Acclimatization:
These cities are not located at high altitudes, so acclimatization should not be an issue.

Accommodation and Booking:
Various types of accommodation are available catering to all budgets. It's advisable to book in advance, especially during peak seasons to secure the best places.

Clothing and Essentials:
Light casual clothing is suitable for the daytime in hotter months, with a jacket for cooler evenings. Don't forget your hats, sunglasses, and sunscreen.

Health and Safety:
Australia has high health standards. Tap water is potable and hygienic food shouldn’t be an issue. Do carry a basic first aid kit. Be aware of any local wildlife that can pose a danger and take precautions.

Local Etiquette and Respect:
Australians are friendly and laid-back, but they appreciate politeness. Respect the local customs and traditions, especially when visiting Aboriginal Land or meeting local Aboriginal people. Always ask for permission before taking photographs on Aboriginal Land or of Aboriginal people.

Lastly, do not forget to sample local wines in Mildura and Renmark, get a riverboat tour in Echuca and enjoy the beachside in Adelaide.