Spanish often uses the definite article more than English does. El hombre means the man.
You usually need an article before a singular countable noun unless there is some special reason not to use one.
Compare:
So el is there because the sentence refers to a specific man.
Because it agrees with el hombre, which is masculine singular.
Spanish adjectives usually agree in gender and number with the noun they describe:
Agreement is a key part of Spanish grammar.
Only if the context already makes it clear who you mean.
For example, if everyone knows you are talking about the man, you could say:
Spanish often drops the subject pronoun, but here el hombre is not a pronoun; it is the full noun phrase the man. You can omit it only when the context already identifies the person.
Not exactly as one fixed chunk, but más o menos is a very common expression that can modify many things.
You can use it with:
So in this sentence, the especially common part is más o menos.
Yes, it sounds natural. A Spaniard might say it when someone is nearly prepared but not completely.
Very natural alternatives could also be:
But está más o menos listo is perfectly normal and understandable.