Sure, I'd be happy to provide you with travel tips for visiting Moscow, Irkutsk, and Vladivostok:

Best Time to Visit:
The best time to visit these Russian cities is during the summer months of June to August when the weather is warm and the days are long. If you are interested in experiencing the winter wonderland, December to February would be an ideal time.

Route and Accessibility:
Flights are available from major cities to Moscow. From Moscow, domestic flights operate regularly to Irkutsk and Vladivostok. Long-haul trains, including the Trans-Siberian Railway, are also available if you prefer a scenic journey.

Altitude and Acclimatization:
Altitude sickness won't be an issue in these cities as they are quite low-lying. However, adapting to the cold temperatures in winter might take some time if you're not used to such severe conditions.

Accommodation and Booking:
It's recommended to book your accommodation in advance, especially during peak travel season (summer months). Options range from luxury hotels to budget hostels.

Clothing and Essentials:
In summer, light clothing is adequate but carry a jacket for the cool evenings. For winter, thermal clothing, a heavy coat, gloves, boots, and a hat are essential. Don't forget your camera for capturing the stunning Siberian landscapes, and a power converter as Russia uses 220-volt electricity with two-round-pin outlets.

Health and Safety:
It is advisable to get travel insurance before your trip. Carry enough medication if you have a prescription. Russia is generally safe but like anywhere, look out for your belongings.

Local Etiquette and Respect:
Russians value their traditions and culture. When visiting churches, women are often required to cover their heads and everyone should dress modestly. Respect the local traditions, be aware of your actions, and try to learn a few basic Russian phrases to interact with locals.