Expanding truly random key into printable password for successive hashing
Q1.
 Each printable ASCII character gives you $\log_2 M$ bits of security where $M$ is the number of printable characters, assuming uniformity and independence between the characters [the second assumption does not hold in natural language]. 

For ASCII $M=106,$ which gives approximately $6.74$ bits/character, but this is likely to be a massive overestimate of security unless a good randomness source is used to
generate the passwords.

Q2. If you want to use limited entropy to generate astronger password you should consider generating a key using a KDF (Key Derivation Function). Have a look at this question and other linked questions from there. Some such schemes are used to derive different passwords/keys for different sites, where the sitename seems to correspond to the message in your case [i.e., it is variable].