Absolutely, planning a trip to London, Cardiff and Edinburgh is a great choice. These cities are a cultural cornucopia and there is something to see and do for everyone.

Best Time to Visit:
The best time to visit these cities would be during spring (late March to June) and fall (September to November). The weather during these times is pleasant and the crowds are relatively thinner.

Route and Accessibility:
London is well connected by flights from all major cities around the world. From London, you can take a train or flight to Cardiff which takes around 2 hours. Another 2 hour train journey north will take you to Edinburgh.

Altitude and Acclimatization:
Thankfully, altitude sickness is not a concern in these cities as the elevation is low. But due to the temperate maritime climate, the weather can be unpredictable and can change quickly, so always check the local forecast.

Accommodation and Booking:
All three cities have a wide range of accommodation options catering to different budget levels. It is highly recommended to book your accommodation well in advance.

Clothing and Essentials:
Depending on the season of your visit, pack appropriate clothing. Always carry an umbrella or raincoat as it can rain any time of year, especially in London and Edinburgh.

Health and Safety:
Stay vigilant while travelling, especially in crowded tourist areas and public transport, where pickpocketing can occur. Also, the UK has strict drinking laws, be aware of them to avoid any problems.

Local Etiquette and Respect:
The British people regard politeness and patience as important virtues. Do not jump queues and always say 'please’ and 'thank you'. In restaurants, tipping is customary, usually 10% of the bill.

Hope these tips help you in planning a fulfilling trip. Safe travels!