Cindy20 0 Newbie Poster

Can you help me decrypt the message with the given information. I figured out the first line is using Xor ciphers but how do I figure out the rest?

Ogaqkxpgbqbfiof! Cyw'ss bun!
Zqksxl cywd lnepwvs uozneh.
Qjc mgabiy nfx vmz-djrhkfalfq.
Xnjfx ai qjvi viqi uat pgw odjwp.
The radio operators have some information that they share with you, in their attempt to decrypt the message. The information is as follows:
‐ The first character of the entire message decrypts to the number ‘5’.
‐ It is known that the first line of the message forms some sort of combined encryption key that is
required to decrypt the rest of the message.
‐ Special characters and spaces are not encrypted in the message. They can be skipped.
‐ XOR encryption was not done on the entire message but all other forms of numerical conversion
and encryption are possibly used within the message.
‐ The use of upper‐case and lower‐case characters in the message are important for decryption.