Certainly! Planning a trip across Singapore, Kuala Lumpur, and Bangkok is an exciting venture. Here's some information that will come in handy:

Best Time to Visit:
The best time to visit Singapore and Kuala Lumpur is from February to April while the best time to visit Bangkok is from November to early April to avoid heavy rains and humid climate.

Route and Accessibility:
Begin your journey with Singapore, then you can take a flight to Kuala Lumpur, which is just an hour away. From Kuala Lumpur, you can choose either a train or flight to reach Bangkok. Plenty of airlines have scheduled flights to these cities.

Altitude and Acclimatization:
This is not a major issue in these cities as they don’t exist on a significant altitude but yes, adjusting to the humid climate might take a bit of time.

Accommodation and Booking:
These are popular tourist destinations, and booking in advance is recommended to avoid last-minute price hikes. A wide range of accommodations are available suiting different budgets, from luxury hotels to backpacker hostels.

Clothing and Essentials:
Light, breathable clothing is recommended as these areas are tropical. Don't forget to pack swimwear, a good sunscreen, a hat, and sunglasses. Carry a comfortable pair of walking shoes as you will be exploring city attractions.

Health and Safety:
Make sure that you're up-to-date on routine vaccines before your trip. Also, get travel insurance as medical treatment can be expensive. Stay hydrated and be wary of street food, especially if you are not used to it.

Local Etiquette and Respect:
In all three cities, it's important to respect local customs and practices. For example, show respect towards monarchy in Thailand and avoid chewing gum in Singapore. Dress modestly when visiting religious and revered sites.

Enjoy your trip!