the reason for "fa" is that you use it together with "caldo". So instead of "è caldo" italians say "fa caldo".
True, from what I have learned from other resources.
Italians literally ask what the weather "makes", not what the weather "is". "Che tempo fa oggi?" translates literally to "What does the weather make today?", figuratively, "What is the weather today?".
The answer to this would be "Fa caldo oggi" (it makes hot today --> it's hot today), or "Fa bello" (it makes nice --> it's nice) etc. The weather is implied, in that you don't have to add "tempo" into the answers.
if 'piuttosto' means 'instead' then where is the logic to translate it to 'pretty'?
Here's how my dictionary translates 'piuttosto': rather, quite, kind of, preferably. There's no 'instead'. Obviously, 'preferably' can't be used in our situation, but it can (as well as 'instead') help to understand the following sentences:
Prenderei piuttosto un tè. Dimmi piuttosto come è andato il viaggio. Dovresti restare piuttosto che partire.
That's a lot more formal nowadays. "Pretty" would be used more often in conversational speech.
For any French speakers out there "piuttosto" appears to be a direct equivalent to "plutôt" :)
This was difficult to translate especially when your own translation was awkward.
I learned somewhere here that when speaking about weather, Italian's use "fare" as oppose to the essere or stare. I think it's because the weather is doing something instead of it is something....could be wrong though
The use of "piuttoste" translates better to "rather", so the answer to your question is no.
"It is really hot" would be "fa veramente caldo qui".
The translation is literally: It is rather hot here. I don't get why DL does not present actual meanings and usage of words so vocabulary can be learned then applied to a context.