There isn't really a 'best' website to look for flights. Tickets change all the time, and the price really depends on how far ahead you are booking. You can keep and eye on different websites, but from experience the best airline to travel with is Turkish Air. One thing for sure, make sure to fly to Skopje, North Macedonia. :)
That is always your preference. One thing about Macedonia is that you can find very affordable apartments, houses and rooms to rent while vacating. You can find such places to stay on Expedia, Booking, Arbnb Web, etc. If you want to stay close to where we will be, look for places in Kumanovo, but if you are planning on staying in the capitol (which is 20 min away), you can look for places in Skopje.
Formal attire is recommended, suits for men and dresses for women. Please do not wear white.