I'm trying to use HKDF after Diffie-Hellman key exchange. However, I got stuck on the HKDF part. 

    from Crypto.Protocol import HKDF
    from Crypto.Hash import SHA512
    from Crypto.Random import get_random_bytes
    
    salt = get_random_bytes(16)
    key1, key2 = HKDF(master_secret, 32, salt, SHA512, 2)

From my understanding, I only need one key for ChaCha20 or AES-256-GCM. Is it a good idea if I only generate one key by HKDF?

One more thing, how can I generate a good salt for this case?