Hello, that sounds like an exciting trip to Poland you're planning! Here are some travel tips for your journey:

Best Time to Visit:
The best time to visit Poland is during late spring (May - June) and early autumn (September - October) when temperatures are comfortable and the tourist crowds are smaller. Nevertheless, the summer months (July - August) are also lovely despite being a bit busier.

Route and Accessibility:
Most international travelers arrive in Poland via Warsaw or Krakow, from there, you can reach Wroclaw, Opole, and Katowice by train or bus. The rail and road networks are well-connected and efficient; rail is often the fastest and most comfortable way to travel between cities.

Accommodation and Booking:
There is a variety of accommodation options in those cities, including hotels, guest houses and, increasingly, vacation rentals. It's recommended to book your accommodation in advance, especially during the summer season. Make use of online booking platforms to compare prices and locations.

Clothing and Essentials:
Polish weather can be quite changeable, so layering is the way to go. Always pack an umbrella and rain jacket just in case. In summer, add light clothing, sunglasses, and sunscreen. For the colder months, bring warm clothing and a good quality winter coat. Comfortable walking shoes are essential to explore the cities.

Health and Safety:
Poland is generally a safe country, but as with any travel, it's a good idea to have travel insurance. Remember to bring any necessary prescription medications and a basic first aid kit. Always stay alert and keep an eye on your belongings in public places.

Local Etiquette and Respect:
Certainly, Polish people value politeness and good manners. Shake hands when meeting people and remember to say please (Proszę) and thank you (Dziękuję). Churches are places of worship, so dress modestly and behave respectfully when visiting.