Sure, I'd be pleased to help with your travel plans to Ioánnina, Párga, and Thessaloníki in Greece.

Best Time to Visit:
The best time to visit Ioánnina, Párga, and Thessaloníki in Greece is during spring (April to early-June) and autumn (September to November). These seasons offer pleasant weather with fewer crowds. The summers (July and August) can get very hot and crowded.

Route and Accessibility:
You can reach Ioánnina by flying into Ioannina National Airport from major European cities with connecting flights. From there, Parga is about 100km away and is accessible by bus or car. Thessaloniki is further east and reachable by train, bus, or car.

Accommodation and Booking:
You will find a wide range of accommodations in these cities, from luxury hotels to affordable guesthouses. It's recommended to book your accommodation in advance, especially during the peak season. You can book via online portals like Booking.com, Airbnb or directly through hotel websites.

Clothing and Essentials:
Pack casual summer clothing for the warm months, and warmer clothes for spring and autumn. Always bring a hat, sunblock, and sunglasses to protect against the sun. Don't forget to pack comfortable shoes for sightseeing.

Health and Safety:
Healthcare facilities are good in Greek cities. However, don't forget to take out travel insurance for any unexpected incidents. Tap water is generally safe to drink. As with any travel, always be cautious of your personal belongings.

Local Etiquette and Respect:
Greeks are very welcoming and friendly. Shake hands when you meet someone. It's common to greet people with a 'Yasas' (Hello). Tipping is customary in Greece, usually around 5-10% of your bill.